Continuity lets you receive and make calls on your Mac and iPad via your iPhone. Previously the feature required your devices to be on the same Wi-Fi network; however, today T-Mobile revealed that Continuity support has been added to its cellular network, letting a Mac or iPad receive an iPhone's call even if it isn't on the same Wi-Fi network.
"T-Mobile customers will be able to answer that important text message or call on your Mac or iPad even if you left your phone at home," says T-Mobile, so "you can leave your phone on your desk and just take your tablet or your Mac to your meeting and never worry about missing anything."
"Customers will need the iOS 9 beta to use the new feature, and it will be available to every T-Mobile customer with an iOS device later this year when iOS 9 is publicly available."
The settings in iOS 9 have been updated to reflect the feature's new capabilities. There's a switch for "Calls on Other Devices" and the ability to individually toggle which devices to allow calls on.
T-Mobile notes that "while others will get on the bandwagon", it's "proud to be the only mobile operator in the world working with Apple to have the new Continuity feature on our network in the iOS 9 beta."