diff --git a/apps/web/lib/orgMigration.ts b/apps/web/lib/orgMigration.ts
index a315be2928..68d8863af1 100644
--- a/apps/web/lib/orgMigration.ts
+++ b/apps/web/lib/orgMigration.ts
@@ -1,6 +1,5 @@
 import { getOrgUsernameFromEmail } from "@calcom/features/auth/signup/utils/getOrgUsernameFromEmail";
 import { getOrgFullOrigin } from "@calcom/features/ee/organizations/lib/orgDomains";
-import { isOrganization } from "@calcom/lib/entityPermissionUtils";
 import { HttpError } from "@calcom/lib/http-error";
 import logger from "@calcom/lib/logger";
 import { safeStringify } from "@calcom/lib/safeStringify";
@@ -48,7 +47,7 @@ export async function moveUserToOrg({
 
   const teamMetadata = teamMetadataSchema.parse(team?.metadata);
 
-  if (!isOrganization({ team })) {
+  if (!team.isOrganization) {
     throw new Error(`Team with ID:${targetOrgId} is not an Org`);
   }
 
@@ -197,7 +196,7 @@ export async function moveTeamToOrg({
 
   const teamMetadata = teamMetadataSchema.parse(possibleOrg?.metadata);
 
-  if (!isOrganization({ team: possibleOrg })) {
+  if (!possibleOrg.isOrganization) {
     throw new Error(`${targetOrg.id} is not an Org`);
   }
 
@@ -667,7 +666,7 @@ async function moveTeamsWithoutMembersToOrg({
       };
     })
     // Remove Orgs from the list
-    .filter((team) => !isOrganization({ team }));
+    .filter((team) => !team.isOrganization);
 
   const teamIdsToBeMovedToOrg = teamsToBeMovedToOrg.map((t) => t.id);
 
@@ -832,7 +831,7 @@ async function removeTeamsWithoutItsMemberFromOrg({ userToRemoveFromOrg }: { use
       };
     })
     // Remove Orgs from the list
-    .filter((team) => !isOrganization({ team }));
+    .filter((team) => !team.isOrganization);
 
   const teamIdsToBeRemovedFromOrg = teamsToBeRemovedFromOrg.map((t) => t.id);
 
diff --git a/apps/web/playwright/change-username.e2e.ts b/apps/web/playwright/change-username.e2e.ts
index 46bf03e778..d92b58196d 100644
--- a/apps/web/playwright/change-username.e2e.ts
+++ b/apps/web/playwright/change-username.e2e.ts
@@ -2,6 +2,9 @@ import { expect } from "@playwright/test";
 
 import stripe from "@calcom/features/ee/payments/server/stripe";
 import { WEBAPP_URL } from "@calcom/lib/constants";
+import { MembershipRole } from "@calcom/prisma/enums";
+
+import { moveUserToOrg } from "@lib/orgMigration";
 
 import { test } from "./lib/fixtures";
 
@@ -110,4 +113,54 @@ test.describe("Change username on settings", () => {
 
     await expect(page).toHaveURL(/.*checkout.stripe.com/);
   });
+
+  test("User can't take a username that has been migrated to a different username in an organization", async ({
+    users,
+    orgs,
+    page,
+  }) => {
+    const existingUser =
+      await test.step("Migrate user to a different username in an organization", async () => {
+        const org = await orgs.create({
+          name: "TestOrg",
+        });
+
+        const existingUser = await users.create({
+          username: "john",
+          emailDomain: org.organizationSettings?.orgAutoAcceptEmail ?? "",
+          name: "John Outside Organization",
+        });
+
+        await moveUserToOrg({
+          user: existingUser,
+          targetOrg: {
+            // Changed username. After this there is no user with username equal to {existingUser.username}
+            username: `${existingUser.username}-org`,
+            id: org.id,
+            membership: {
+              role: MembershipRole.MEMBER,
+              accepted: true,
+            },
+          },
+          shouldMoveTeams: false,
+        });
+        return existingUser;
+      });
+
+    await test.step("Changing username for another user to the previous username of migrated user - shouldn't be allowed", async () => {
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      const previousUsername = existingUser.username!;
+
+      const user = await users.create();
+      await user.apiLogin();
+
+      await page.goto("/settings/my-account/profile");
+      const usernameInput = page.locator("[data-testid=username-input]");
+
+      await usernameInput.fill(previousUsername);
+      await page.waitForLoadState("networkidle");
+      await expect(page.locator("[data-testid=update-username-btn]").nth(0)).toBeHidden();
+      await expect(page.locator("[data-testid=update-username-btn]").nth(1)).toBeHidden();
+    });
+  });
 });
diff --git a/apps/web/playwright/fixtures/users.ts b/apps/web/playwright/fixtures/users.ts
index b5f85b35b6..faa18a20ed 100644
--- a/apps/web/playwright/fixtures/users.ts
+++ b/apps/web/playwright/fixtures/users.ts
@@ -604,15 +604,33 @@ const createUserFixture = (user: UserWithIncludes, page: Page) => {
       return membership;
     },
     getOrgMembership: async () => {
-      return prisma.membership.findFirstOrThrow({
+      const membership = await prisma.membership.findFirstOrThrow({
         where: {
           userId: user.id,
           team: {
             isOrganization: true,
           },
         },
-        include: { team: { include: { children: true } } },
+        include: {
+          team: {
+            include: {
+              children: true,
+              organizationSettings: true,
+            },
+          },
+        },
       });
+      if (!membership) {
+        return membership;
+      }
+
+      return {
+        ...membership,
+        team: {
+          ...membership.team,
+          metadata: teamMetadataSchema.parse(membership.team.metadata),
+        },
+      };
     },
     getFirstEventAsOwner: async () =>
       prisma.eventType.findFirstOrThrow({
@@ -670,6 +688,7 @@ type CustomUserOpts = Partial<Pick<Prisma.User, CustomUserOptsKeys>> & {
   roleInOrganization?: MembershipRole;
   schedule?: Schedule;
   password?: string | null;
+  emailDomain?: string;
 };
 
 // creates the actual user in the db.
@@ -687,10 +706,11 @@ const createUser = (
       ? opts.username
       : `${opts?.username || "user"}-${workerInfo.workerIndex}-${Date.now()}`;
 
+  const emailDomain = opts?.emailDomain || "example.com";
   return {
     username: uname,
     name: opts?.name,
-    email: opts?.email ?? `${uname}@example.com`,
+    email: opts?.email ?? `${uname}@${emailDomain}`,
     password: {
       create: {
         hash: hashPassword(uname),
diff --git a/apps/web/playwright/organization/organization-invitation.e2e.ts b/apps/web/playwright/organization/organization-invitation.e2e.ts
index 1b3eac6949..80e275b9c3 100644
--- a/apps/web/playwright/organization/organization-invitation.e2e.ts
+++ b/apps/web/playwright/organization/organization-invitation.e2e.ts
@@ -2,6 +2,9 @@ import type { Browser, Page } from "@playwright/test";
 import { expect } from "@playwright/test";
 
 import prisma from "@calcom/prisma";
+import { MembershipRole } from "@calcom/prisma/client";
+
+import { moveUserToOrg } from "@lib/orgMigration";
 
 import { test } from "../lib/fixtures";
 import { getInviteLink } from "../lib/testUtils";
@@ -16,7 +19,7 @@ test.afterEach(async ({ users, orgs }) => {
 
 test.describe("Organization", () => {
   test.describe("Email not matching orgAutoAcceptEmail", () => {
-    test("Org Invitation", async ({ browser, page, users, emails }) => {
+    test("nonexisting user invited to an organization", async ({ browser, page, users, emails }) => {
       const orgOwner = await users.create(undefined, { hasTeam: true, isOrg: true });
       const { team: org } = await orgOwner.getOrgMembership();
       await orgOwner.apiLogin();
@@ -83,7 +86,17 @@ test.describe("Organization", () => {
       });
     });
 
-    test("Team invitation", async ({ browser, page, users, emails }) => {
+    // This test is already covered by booking.e2e.ts where existing user is invited and his booking links are tested.
+    // We can re-test here when we want to test some more scenarios.
+    // eslint-disable-next-line @typescript-eslint/no-empty-function
+    test("existing user invited to an organization", () => {});
+
+    test("nonexisting user invited to a Team inside organization", async ({
+      browser,
+      page,
+      users,
+      emails,
+    }) => {
       const orgOwner = await users.create(undefined, { hasTeam: true, isOrg: true, hasSubteam: true });
       await orgOwner.apiLogin();
       const { team } = await orgOwner.getFirstTeamMembership();
@@ -183,7 +196,7 @@ test.describe("Organization", () => {
   });
 
   test.describe("Email matching orgAutoAcceptEmail and a Verified Organization", () => {
-    test("Org Invitation", async ({ browser, page, users, emails }) => {
+    test("nonexisting user is invited to Org", async ({ browser, page, users, emails }) => {
       const orgOwner = await users.create(undefined, { hasTeam: true, isOrg: true, isOrgVerified: true });
       const { team: org } = await orgOwner.getOrgMembership();
       await orgOwner.apiLogin();
@@ -248,7 +261,52 @@ test.describe("Organization", () => {
       });
     });
 
-    test("Team Invitation", async ({ browser, page, users, emails }) => {
+    // Such a user has user.username changed directly in addition to having the new username in the profile.username
+    test("existing user migrated to an organization", async ({ users, page, emails }) => {
+      const orgOwner = await users.create(undefined, { hasTeam: true, isOrg: true, isOrgVerified: true });
+      const { team: org } = await orgOwner.getOrgMembership();
+      await orgOwner.apiLogin();
+      const { existingUser } = await test.step("Invite an existing user to an organization", async () => {
+        const existingUser = await users.create({
+          username: "john",
+          emailDomain: org.organizationSettings?.orgAutoAcceptEmail ?? "",
+          name: "John Outside Organization",
+        });
+
+        await moveUserToOrg({
+          user: existingUser,
+          targetOrg: {
+            username: `${existingUser.username}-org`,
+            id: org.id,
+            membership: {
+              role: MembershipRole.MEMBER,
+              accepted: true,
+            },
+          },
+          shouldMoveTeams: false,
+        });
+        return { existingUser };
+      });
+
+      await test.step("Signing up with the previous username of the migrated user - shouldn't be allowed", async () => {
+        await page.goto("/signup");
+        // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+        await page.locator('input[name="username"]').fill(existingUser.username!);
+        await page
+          .locator('input[name="email"]')
+          .fill(`${existingUser.username}-differnet-email@example.com`);
+        await page.locator('input[name="password"]').fill("Password99!");
+        await page.waitForLoadState("networkidle");
+        await expect(page.locator('button[type="submit"]')).toBeDisabled();
+      });
+    });
+
+    test("nonexisting user is invited to a team inside organization", async ({
+      browser,
+      page,
+      users,
+      emails,
+    }) => {
       const orgOwner = await users.create(undefined, {
         hasTeam: true,
         isOrg: true,
diff --git a/packages/features/auth/signup/handlers/calcomHandler.ts b/packages/features/auth/signup/handlers/calcomHandler.ts
index 6104c71660..8cec77bde4 100644
--- a/packages/features/auth/signup/handlers/calcomHandler.ts
+++ b/packages/features/auth/signup/handlers/calcomHandler.ts
@@ -8,6 +8,7 @@ import { createOrUpdateMemberships } from "@calcom/features/auth/signup/utils/cr
 import { WEBAPP_URL } from "@calcom/lib/constants";
 import { getLocaleFromRequest } from "@calcom/lib/getLocaleFromRequest";
 import { HttpError } from "@calcom/lib/http-error";
+import logger from "@calcom/lib/logger";
 import { usernameHandler, type RequestWithUsernameStatus } from "@calcom/lib/server/username";
 import { createWebUser as syncServicesCreateWebUser } from "@calcom/lib/sync/SyncServiceManager";
 import { closeComUpsertTeamUser } from "@calcom/lib/sync/SyncServiceManager";
@@ -23,6 +24,8 @@ import {
   validateAndGetCorrectedUsernameForTeam,
 } from "../utils/token";
 
+const log = logger.getSubLogger({ prefix: ["signupCalcomHandler"] });
+
 async function handler(req: RequestWithUsernameStatus, res: NextApiResponse) {
   const {
     email: _email,
@@ -35,6 +38,9 @@ async function handler(req: RequestWithUsernameStatus, res: NextApiResponse) {
       token: true,
     })
     .parse(req.body);
+
+  log.debug("handler", { email: _email });
+
   let username: string | null = req.usernameStatus.requestedUserName;
   let checkoutSessionId: string | null = null;
 
diff --git a/packages/features/auth/signup/handlers/selfHostedHandler.ts b/packages/features/auth/signup/handlers/selfHostedHandler.ts
index 9fd6373496..d24b750044 100644
--- a/packages/features/auth/signup/handlers/selfHostedHandler.ts
+++ b/packages/features/auth/signup/handlers/selfHostedHandler.ts
@@ -6,6 +6,7 @@ import { sendEmailVerification } from "@calcom/features/auth/lib/verifyEmail";
 import { createOrUpdateMemberships } from "@calcom/features/auth/signup/utils/createOrUpdateMemberships";
 import { IS_PREMIUM_USERNAME_ENABLED } from "@calcom/lib/constants";
 import logger from "@calcom/lib/logger";
+import { isUsernameReservedDueToMigration } from "@calcom/lib/server/username";
 import slugify from "@calcom/lib/slugify";
 import { closeComUpsertTeamUser } from "@calcom/lib/sync/SyncServiceManager";
 import { validateAndGetCorrectedUsernameAndEmail } from "@calcom/lib/validateUsername";
@@ -78,7 +79,19 @@ export default async function handler(req: NextApiRequest, res: NextApiResponse)
         organizationSettings: true,
       },
     });
+
     if (team) {
+      const isInviteForATeamInOrganization = !!team.parent;
+      const isCheckingUsernameInGlobalNamespace = !team.isOrganization && !isInviteForATeamInOrganization;
+
+      if (isCheckingUsernameInGlobalNamespace) {
+        const isUsernameAvailable = !(await isUsernameReservedDueToMigration(correctedUsername));
+        if (!isUsernameAvailable) {
+          res.status(409).json({ message: "A user exists with that username" });
+          return;
+        }
+      }
+
       const user = await prisma.user.upsert({
         where: { email: userEmail },
         update: {
@@ -123,6 +136,11 @@ export default async function handler(req: NextApiRequest, res: NextApiResponse)
       },
     });
   } else {
+    const isUsernameAvailable = !(await isUsernameReservedDueToMigration(correctedUsername));
+    if (!isUsernameAvailable) {
+      res.status(409).json({ message: "A user exists with that username" });
+      return;
+    }
     if (IS_PREMIUM_USERNAME_ENABLED) {
       const checkUsername = await checkPremiumUsername(correctedUsername);
       if (checkUsername.premium) {
diff --git a/packages/features/ee/teams/components/TeamListItem.tsx b/packages/features/ee/teams/components/TeamListItem.tsx
index e66c8cadd6..f3beadc1ec 100644
--- a/packages/features/ee/teams/components/TeamListItem.tsx
+++ b/packages/features/ee/teams/components/TeamListItem.tsx
@@ -6,7 +6,6 @@ import InviteLinkSettingsModal from "@calcom/ee/teams/components/InviteLinkSetti
 import MemberInvitationModal from "@calcom/ee/teams/components/MemberInvitationModal";
 import classNames from "@calcom/lib/classNames";
 import { getPlaceholderAvatar } from "@calcom/lib/defaultAvatarImage";
-import { isOrganization } from "@calcom/lib/entityPermissionUtils";
 import { getTeamUrlSync } from "@calcom/lib/getBookerUrl/client";
 import { useCompatSearchParams } from "@calcom/lib/hooks/useCompatSearchParams";
 import { useLocale } from "@calcom/lib/hooks/useLocale";
@@ -77,7 +76,7 @@ export default function TeamListItem(props: Props) {
       utils.viewer.teams.listInvites.invalidate();
       const userOrganizationId = user?.profile?.organization?.id;
       const isSubTeamOfDifferentOrg = team.parentId ? team.parentId != userOrganizationId : false;
-      const isDifferentOrg = isOrganization({ team }) && team.id !== userOrganizationId;
+      const isDifferentOrg = team.isOrganization && team.id !== userOrganizationId;
       // If the user team being accepted is a sub-team of different organization or the different organization itself then page must be reloaded to let the session change reflect reliably everywhere.
       if (variables.accept && (isSubTeamOfDifferentOrg || isDifferentOrg)) {
         window.location.reload();
@@ -101,7 +100,7 @@ export default function TeamListItem(props: Props) {
   const { hideDropdown, setHideDropdown } = props;
 
   if (!team) return <></>;
-  const teamUrl = isOrganization({ team })
+  const teamUrl = team.isOrganization
     ? getTeamUrlSync({ orgSlug: team.slug, teamSlug: null })
     : getTeamUrlSync({ orgSlug: team.parent ? team.parent.slug : null, teamSlug: team.slug });
   const teamInfo = (
diff --git a/packages/features/ee/teams/components/TeamsListing.tsx b/packages/features/ee/teams/components/TeamsListing.tsx
index b10fc62374..6565939568 100644
--- a/packages/features/ee/teams/components/TeamsListing.tsx
+++ b/packages/features/ee/teams/components/TeamsListing.tsx
@@ -2,7 +2,6 @@ import { useRouter } from "next/navigation";
 import { useEffect, useMemo, useState } from "react";
 
 import { APP_NAME, WEBAPP_URL } from "@calcom/lib/constants";
-import { isOrganization } from "@calcom/lib/entityPermissionUtils";
 import { useCompatSearchParams } from "@calcom/lib/hooks/useCompatSearchParams";
 import { useLocale } from "@calcom/lib/hooks/useLocale";
 import { trpc } from "@calcom/trpc/react";
@@ -46,14 +45,11 @@ export function TeamsListing() {
     },
   });
 
-  const teams = useMemo(() => data?.filter((m) => m.accepted && !isOrganization({ team: m })) || [], [data]);
+  const teams = useMemo(() => data?.filter((m) => m.accepted && !m.isOrganization) || [], [data]);
 
-  const teamInvites = useMemo(
-    () => data?.filter((m) => !m.accepted && !isOrganization({ team: m })) || [],
-    [data]
-  );
+  const teamInvites = useMemo(() => data?.filter((m) => !m.accepted && !m.isOrganization) || [], [data]);
 
-  const organizationInvites = (data?.filter((m) => !m.accepted && isOrganization({ team: m })) || []).filter(
+  const organizationInvites = (data?.filter((m) => !m.accepted && m.isOrganization) || []).filter(
     (orgInvite) => {
       const isThereASubTeamOfTheOrganizationInInvites = teamInvites.find(
         (teamInvite) => teamInvite.parentId === orgInvite.id
diff --git a/packages/features/ee/teams/lib/payments.ts b/packages/features/ee/teams/lib/payments.ts
index e6f4dae9e2..ed543d2120 100644
--- a/packages/features/ee/teams/lib/payments.ts
+++ b/packages/features/ee/teams/lib/payments.ts
@@ -4,7 +4,6 @@ import { getStripeCustomerIdFromUserId } from "@calcom/app-store/stripepayment/l
 import stripe from "@calcom/app-store/stripepayment/lib/server";
 import { WEBAPP_URL } from "@calcom/lib/constants";
 import { ORGANIZATION_MIN_SEATS } from "@calcom/lib/constants";
-import { isOrganization } from "@calcom/lib/entityPermissionUtils";
 import prisma from "@calcom/prisma";
 import { teamMetadataSchema } from "@calcom/prisma/zod-utils";
 
@@ -157,7 +156,7 @@ export const updateQuantitySubscriptionFromStripe = async (teamId: number) => {
     )?.quantity;
     if (!subscriptionQuantity) throw new Error("Subscription not found");
 
-    if (!!isOrganization({ team }) && membershipCount < ORGANIZATION_MIN_SEATS) {
+    if (team.isOrganization && membershipCount < ORGANIZATION_MIN_SEATS) {
       console.info(
         `Org ${teamId} has less members than the min ${ORGANIZATION_MIN_SEATS}, skipping updating subscription.`
       );
diff --git a/packages/lib/entityPermissionUtils.ts b/packages/lib/entityPermissionUtils.ts
index d08dce51dd..6031c0a50b 100644
--- a/packages/lib/entityPermissionUtils.ts
+++ b/packages/lib/entityPermissionUtils.ts
@@ -1,4 +1,4 @@
-import type { Membership, Team } from "@calcom/prisma/client";
+import type { Membership } from "@calcom/prisma/client";
 import { MembershipRole } from "@calcom/prisma/enums";
 
 export const enum ENTITY_PERMISSION_LEVEL {
@@ -19,10 +19,6 @@ export function canEditEntity(
   );
 }
 
-export function isOrganization({ team }: { team: Pick<Team, "isOrganization"> }) {
-  return team.isOrganization;
-}
-
 export function getEntityPermissionLevel(
   entity: {
     userId: number | null;
diff --git a/packages/lib/server/checkRegularUsername.ts b/packages/lib/server/checkRegularUsername.ts
index e039091268..964c8c43bf 100644
--- a/packages/lib/server/checkRegularUsername.ts
+++ b/packages/lib/server/checkRegularUsername.ts
@@ -1,8 +1,10 @@
 import slugify from "@calcom/lib/slugify";
 
 import { ProfileRepository } from "./repository/profile";
+import { isUsernameReservedDueToMigration } from "./username";
 
 export async function checkRegularUsername(_username: string, currentOrgDomain?: string | null) {
+  const isCheckingUsernameInGlobalNamespace = !currentOrgDomain;
   const username = slugify(_username);
 
   const premium = !!process.env.NEXT_PUBLIC_IS_E2E && username.length < 5;
@@ -23,8 +25,13 @@ export async function checkRegularUsername(_username: string, currentOrgDomain?:
       message: "A user exists with that username",
     };
   }
+
+  const isUsernameAvailable = isCheckingUsernameInGlobalNamespace
+    ? !(await isUsernameReservedDueToMigration(username))
+    : true;
+
   return {
-    available: true as const,
+    available: isUsernameAvailable,
     premium,
   };
 }
diff --git a/packages/lib/server/checkUsername.ts b/packages/lib/server/checkUsername.ts
index 6c1c31f1c5..1d57927f1e 100644
--- a/packages/lib/server/checkUsername.ts
+++ b/packages/lib/server/checkUsername.ts
@@ -3,4 +3,6 @@ import { IS_PREMIUM_USERNAME_ENABLED } from "@calcom/lib/constants";
 import { checkRegularUsername } from "./checkRegularUsername";
 import { usernameCheck as checkPremiumUsername } from "./username";
 
+// TODO: Replace `lib/checkPremiumUsername` with `usernameCheck` and then import checkPremiumUsername directly here.
+// We want to remove dependency on website for signup stuff as signup is now part of app.
 export const checkUsername = !IS_PREMIUM_USERNAME_ENABLED ? checkRegularUsername : checkPremiumUsername;
diff --git a/packages/lib/server/repository/user.ts b/packages/lib/server/repository/user.ts
index 1864439d0f..5f2ed07f4a 100644
--- a/packages/lib/server/repository/user.ts
+++ b/packages/lib/server/repository/user.ts
@@ -4,7 +4,6 @@ import { Prisma } from "@calcom/prisma/client";
 import type { User as UserType } from "@calcom/prisma/client";
 import type { UpId, UserProfile } from "@calcom/types/UserProfile";
 
-import { isOrganization } from "../../entityPermissionUtils";
 import logger from "../../logger";
 import { safeStringify } from "../../safeStringify";
 import { ProfileRepository } from "./profile";
@@ -92,8 +91,8 @@ export class UserRepository {
       userId,
     });
 
-    const acceptedOrgMemberships = acceptedTeamMemberships.filter((membership) =>
-      isOrganization({ team: membership.team })
+    const acceptedOrgMemberships = acceptedTeamMemberships.filter(
+      (membership) => membership.team.isOrganization
     );
 
     const organizations = acceptedOrgMemberships.map((membership) => membership.team);
diff --git a/packages/lib/server/username.ts b/packages/lib/server/username.ts
index c8bd09df24..b4a01bc580 100644
--- a/packages/lib/server/username.ts
+++ b/packages/lib/server/username.ts
@@ -2,10 +2,13 @@ import type { NextApiRequest, NextApiResponse } from "next";
 
 import slugify from "@calcom/lib/slugify";
 import prisma from "@calcom/prisma";
+import { RedirectType } from "@calcom/prisma/enums";
 
 import { IS_PREMIUM_USERNAME_ENABLED } from "../constants";
+import logger from "../logger";
 import notEmpty from "../notEmpty";
 
+const log = logger.getSubLogger({ prefix: ["server/username"] });
 const cachedData: Set<string> = new Set();
 
 export type RequestWithUsernameStatus = NextApiRequest & {
@@ -106,7 +109,9 @@ const usernameHandler =
     return handler(req, res);
   };
 
-const usernameCheck = async (usernameRaw: string) => {
+const usernameCheck = async (usernameRaw: string, currentOrgDomain?: string | null) => {
+  log.debug("usernameCheck", { usernameRaw, currentOrgDomain });
+  const isCheckingUsernameInGlobalNamespace = !currentOrgDomain;
   const response = {
     available: true,
     premium: false,
@@ -129,6 +134,10 @@ const usernameCheck = async (usernameRaw: string) => {
 
   if (user) {
     response.available = false;
+  } else {
+    response.available = isCheckingUsernameInGlobalNamespace
+      ? !(await isUsernameReservedDueToMigration(username))
+      : true;
   }
 
   if (await isPremiumUserName(username)) {
@@ -158,6 +167,20 @@ const usernameCheck = async (usernameRaw: string) => {
   return response;
 };
 
+/**
+ * Should be used when in global namespace(i.e. outside of an organization)
+ */
+export const isUsernameReservedDueToMigration = async (username: string) =>
+  !!(await prisma.tempOrgRedirect.findUnique({
+    where: {
+      from_type_fromOrgId: {
+        type: RedirectType.User,
+        from: username,
+        fromOrgId: 0,
+      },
+    },
+  }));
+
 /**
  * It is a bit different from usernameCheck because it also check if the user signing up is the same user that has a pending invitation to organization
  * So, it uses email to uniquely identify the user and then also checks if the username requested by that user is available for taking or not.
@@ -207,12 +230,13 @@ const usernameCheckForSignup = async ({
       const isClaimingAlreadySetUsername = user.username === username;
       const isClaimingUnsetUsername = !user.username;
       response.available = isClaimingUnsetUsername || isClaimingAlreadySetUsername;
-      // There are no premium users outside an organization only
+      // There are premium users outside an organization only
       response.premium = await isPremiumUserName(username);
     }
+    // If user isn't found, it's a direct signup and that can't be of an organization
   } else {
-    // If user isn't found, it's a new signup and that can't be of an organization
     response.premium = await isPremiumUserName(username);
+    response.available = !(await isUsernameReservedDueToMigration(username));
   }
 
   // get list of similar usernames in the db
diff --git a/packages/trpc/server/routers/viewer/eventTypes/getByViewer.handler.ts b/packages/trpc/server/routers/viewer/eventTypes/getByViewer.handler.ts
index 0e4fea76bd..eff78baadb 100644
--- a/packages/trpc/server/routers/viewer/eventTypes/getByViewer.handler.ts
+++ b/packages/trpc/server/routers/viewer/eventTypes/getByViewer.handler.ts
@@ -3,7 +3,6 @@ import { orderBy } from "lodash";
 
 import { hasFilter } from "@calcom/features/filters/lib/hasFilter";
 import { checkRateLimitAndThrowError } from "@calcom/lib/checkRateLimitAndThrowError";
-import { isOrganization } from "@calcom/lib/entityPermissionUtils";
 import { getOrgAvatarUrl, getTeamAvatarUrl, getUserAvatarUrl } from "@calcom/lib/getAvatarUrl";
 import { getBookerBaseUrlSync } from "@calcom/lib/getBookerUrl/client";
 import { getBookerBaseUrl } from "@calcom/lib/getBookerUrl/server";
@@ -214,7 +213,7 @@ export const getByViewerHandler = async ({ ctx, input }: GetByViewerOptions) =>
     await Promise.all(
       memberships
         .filter((mmship) => {
-          if (isOrganization({ team: mmship.team })) {
+          if (mmship.team.isOrganization) {
             return false;
           } else {
             if (!input?.filters || !hasFilter(input?.filters)) {
diff --git a/packages/trpc/server/routers/viewer/teams/acceptOrLeave.handler.ts b/packages/trpc/server/routers/viewer/teams/acceptOrLeave.handler.ts
index c15af40206..963c53f5b6 100644
--- a/packages/trpc/server/routers/viewer/teams/acceptOrLeave.handler.ts
+++ b/packages/trpc/server/routers/viewer/teams/acceptOrLeave.handler.ts
@@ -1,5 +1,4 @@
 import { createAProfileForAnExistingUser } from "@calcom/lib/createAProfileForAnExistingUser";
-import { isOrganization } from "@calcom/lib/entityPermissionUtils";
 import { updateNewTeamMemberEventTypes } from "@calcom/lib/server/queries";
 import { closeComUpsertTeamUser } from "@calcom/lib/sync/SyncServiceManager";
 import { prisma } from "@calcom/prisma";
@@ -45,9 +44,8 @@ export const acceptOrLeaveHandler = async ({ ctx, input }: AcceptOrLeaveOptions)
       });
     }
 
-    const isAnOrganization = isOrganization({ team });
     const isASubteam = team.parentId !== null;
-    const idOfOrganizationInContext = isAnOrganization ? team.id : isASubteam ? team.parentId : null;
+    const idOfOrganizationInContext = team.isOrganization ? team.id : isASubteam ? team.parentId : null;
     const needProfileUpdate = !!idOfOrganizationInContext;
     if (needProfileUpdate) {
       await createAProfileForAnExistingUser({
diff --git a/packages/trpc/server/routers/viewer/teams/inviteMember/inviteMember.handler.ts b/packages/trpc/server/routers/viewer/teams/inviteMember/inviteMember.handler.ts
index f6f3a48ed6..5b991dd958 100644
--- a/packages/trpc/server/routers/viewer/teams/inviteMember/inviteMember.handler.ts
+++ b/packages/trpc/server/routers/viewer/teams/inviteMember/inviteMember.handler.ts
@@ -2,7 +2,6 @@ import { updateQuantitySubscriptionFromStripe } from "@calcom/features/ee/teams/
 import { checkRateLimitAndThrowError } from "@calcom/lib/checkRateLimitAndThrowError";
 import { IS_TEAM_BILLING_ENABLED } from "@calcom/lib/constants";
 import { createAProfileForAnExistingUser } from "@calcom/lib/createAProfileForAnExistingUser";
-import { isOrganization } from "@calcom/lib/entityPermissionUtils";
 import logger from "@calcom/lib/logger";
 import { safeStringify } from "@calcom/lib/safeStringify";
 import { getTranslation } from "@calcom/lib/server/i18n";
@@ -174,7 +173,7 @@ async function handleExistingUsersInvites({
   }
 
   const translation = await getTranslation(input.language ?? "en", "common");
-  if (!isOrganization({ team })) {
+  if (!team.isOrganization) {
     const [autoJoinUsers, regularUsers] = groupUsersByJoinability({
       existingUsersWithMembersips,
       team,
diff --git a/packages/trpc/server/routers/viewer/teams/inviteMember/utils.ts b/packages/trpc/server/routers/viewer/teams/inviteMember/utils.ts
index be6b047ce4..dc3adb8025 100644
--- a/packages/trpc/server/routers/viewer/teams/inviteMember/utils.ts
+++ b/packages/trpc/server/routers/viewer/teams/inviteMember/utils.ts
@@ -3,7 +3,6 @@ import type { TFunction } from "next-i18next";
 
 import { sendTeamInviteEmail } from "@calcom/emails";
 import { ENABLE_PROFILE_SWITCHER, WEBAPP_URL } from "@calcom/lib/constants";
-import { isOrganization } from "@calcom/lib/entityPermissionUtils";
 import logger from "@calcom/lib/logger";
 import { safeStringify } from "@calcom/lib/safeStringify";
 import { isTeamAdmin } from "@calcom/lib/server/queries";
@@ -452,7 +451,7 @@ export function getAutoJoinStatus({
   invitee: UserWithMembership;
   connectionInfoMap: Record<string, ReturnType<typeof getOrgConnectionInfo>>;
 }) {
-  const isRegularTeam = !isOrganization({ team }) && !team.parentId;
+  const isRegularTeam = !team.isOrganization && !team.parentId;
 
   if (isRegularTeam) {
     // There are no-auto join in regular teams ever