Apple’s iPhone Handoff feature will not launch everywhere with iOS 27. MacRumors reports that the service will initially work with T-Mobile in the United States and Deutsche Telekom in Germany, making carrier support the key limit for the first release.

iPhone Handoff is designed for people who use two iPhones. The same phone number can be active on both devices, but only one phone can be the main active iPhone at a time. The change happens when the user unlocks the other device.

Apple says both phones must run iOS 27 or later. They must also connect to Wi-Fi and use the same Apple Account. FaceTime, iMessage and Messages in iCloud need to be turned on before the feature can be configured.

The setup can appear during the process of adding a new iPhone. Users can also turn the feature on later in Settings. Apple describes one phone as the main device and the other as the secondary device, with the number switching automatically between them.

Some account functions remain tied to the main iPhone. Apple says call forwarding, caller ID and certain account-management tools may only be managed from that device. Apple Watch also does not move between the two phones when the number changes.

Wallet cards and car keys can work across both devices, but Apple warns that some transit passes, IDs and corporate badges may work on only one iPhone. Users who rely on those items will need to check the device they unlock before leaving home.

Dual-SIM users can use iPhone Handoff when both eSIMs come from supported carriers. Each eSIM must be set up separately, and the two lines switch together when the user moves to the other iPhone.

Apple has not announced T-Mobile pricing. iOS 27 is scheduled to launch on September 14. The restricted start suggests that users in other markets will need to wait for individual carriers to add support before the feature becomes useful to them.