Carrier Cellular Continuity over LTE with iOS9 - T-mobile specific right now

[cariacou]

Wow!

to me, this is the best feature of iOS9 hands on.

with the latest software (iOS9 &/or MacOSX El Capitain), you can now make and receive calls/texts with your phone turned OFF!

this is amazing. you can:
-text from a plane
-make/receive calls from abroad without any surcharge (assuming you have a data connection)
-sell your iPhone and use an iPad mini if you have (very) big hands (and pockets)
-etc...


Official Page:

Place a Wi-Fi call from another device (T-Mobile only)
If you're in the United States and use T-Mobile, you can place a Wi-Fi call from your iPad or iPod touch with iOS 9 or Mac with OS X El Capitan. When you place the call, your iPhone could be right next to you or far away—it could even be off.

To place a Wi-Fi call from your iPad, iPod touch, or Mac, follow these steps:

Call from your iPad, iPod touch, or Mac

1. If you haven't added your device yet—which allows it to use Wi-Fi Calling—add it.
2. Open FaceTime.
3. Tap Audio.
4. Enter a contact or phone number and tap
   
   .

You can also place a call by tapping a phone number in Contacts, Mail, Messages, Safari, and other apps.


https://support.apple.com/en-us/HT203032