AT&T NumberSync WiFi Calling From Other Devices
The iOS 9.2 update adds support for placing a WiFi call from another device through your AT&T smartphone using WiFi calling.
Apple Support documents outline the option to make a Wifi call from the iPad or iPod Touch on iOS 9.2. With this option set up you can, "make Wi-Fi calls with Apple Watch with watchOS 2, 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."
Even though this was not listed in the change log, support documents back up this option. For this to work all devices will need to be on iOS 9.2.