Good news if you're a T-Mobile customer and use Apple devices: You'll be able to handle messages and calls with Apple's Continuity feature even when using the carrier's Wi-Fi calling. Even better, Continuity will work even if devices aren't on the same wireless network.
The change should make T-Mobile subscribers happy.
With iOS 8, Continuity didn't work if your handset was working over Wi-Fi calling instead of a traditional cellular network, reports TMoNews. That means calls and messages coming to your iPhone wouldn't be routed to an iPad or Mac.
With iOS 9 that changes. On Reddit, an iOS 9 beta tester noted that the Wi-Fi calling limitation is gone:
Since iOS 8, T-Mobile iPhone users have been able to use wifi calling. iOS 8 also brought the ability to send and receive all calls on other iOS/Mac devices. These two features could not be used simultaneously.
This issue has been resolved as of iOS 9. I was able to place a phone call on my iPad mini (iOS 8.4 beta 3) over continuity with my iPhone 6 Plus on iOS 9 beta 1 on wifi calling.
I also received an email confirmation from the carrier, which says iOS 9 brings even more to the table for T-Mobile subscribers, however.
Instead of requiring Apple's devices on the same Wi-Fi network for Continuity, the feature will work across T-Mobile's network; "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."
T-Mobile says it's the first, and currently only, carrier to work with Apple to extend Continuity beyond Wi-Fi networks.