AT&T announced a while back about a new service they were going to offer called NumberSync. I honestly just blew it off as another gimicky service that was carrier based so most likely horribly implemented. This week the feature has been enabled on iOS devices along with... WIFI CALLING!!!! These two new features go hand in hand and use each other to work. Let's take a look at setting this up since it can get a bit confusing and took me a few tries to get all figured out (I also just ported my Google Voice number back to a carrier since I have now given up on GVoice after 2+ years of trying to make usable in a multi OS environment). Note: This post will be refined w/screenshots shortly.. :)
1. As of January 22, 2016; iOS devices are only really supported along with Mac OS X computers. Yes, computers. You can make voice and text calls from your mac computer if you have a new iPhone on the latest iOS 9.2 / 9.2.1. Here are the full requirements per AT&T ( IOS Devices )
2. On your iPhone, go to Settings > Phone. Then scroll down to the new feature, Wi-Fi Calling. Tap on it and and then enable it. You will have to go through a EULA/Disclaimer and also setup your address for E911. Once this is done, you will then have Wi-Fi Calling enabled in a few mins; a prompt will popup once enabled.
3. Be sure to be logged into iCloud and iMessage and Facetime w/the same apple id.
4. Back in the Settings > Phone, you should have an option below Wi-Fi Calling called "Calls on Other Devices". Enable it and again go through the disclaimer and once enabled, you will get a prompt.
5. Now we can add devices to in turn send text messages via iMessage as your carrier number and make phone calls. I have noticed that phone calls do not show your caller id number but the quality is on par with and better than Google Voice (i tested with a co-worker this evening from my mac mini and a logitech hd web cam).
6. You also will need to be logged into your iCloud account on your Mac with the same id as on your iPhone and the same in the Messages app on Mac OS X and Facetime on Mac OS X.
7. Back on your iPhone, go to Settings > Messages and then tap on the "Text Message Forwarding" option.
Then go into each app on your Mac and then Preferences and then choose the Accounts tab and the iMessage account. Be sure to set your "Start New Conversations" to your phone number if you want to keep it all synced to your iPhone.