T-Mobile will implement a $5 monthly fee for its iPhone Handoff feature, enabling users to share a single phone number across two iPhones. This e-SIM functionality requires carrier support, with T-Mobile in the U.S. and Deutsche Telekom in Germany as initial providers. T-Mobile customers can seamlessly switch their active phone between two compatible iPhones, with features like calls, texts, and data available on both. The feature is enabled by iOS 27 and subsequent versions, requiring both iPhones to be on the same Apple Account and connected to Wi-Fi. One iPhone acts as the primary, while the other is secondary, with activation shifting automatically upon unlocking either device. While payment cards and car keys can function on both, some Wallet items might be restricted to a single device. iPhone Handoff does not facilitate Apple Watch transfers between iPhones. The feature supports Dual SIM as long as both eSIMs are from supportive carriers, with each needing separate setup. iOS 27 is scheduled for release on September 14, followed by the iPhone 18 Pro models on September 18.