There is not long list of phones that supports VoLTE on AT&T as only flagship phone comes with Voice over LTE. AT&T did post about the information about this update with the today’s date listed and the update will bring HD voice calls along with new Android 4.4.4 Kitkat version and several new Bluetooth enhancement, copy and paste feature for the camera. Other improvements include AMBS Cloud messaging integration, Usage Manager app for phone and improved battery life and AT&T Ready2Go app.
Since the update is sent out in batches, you might not see the update notification on your device. If you can’t hold your patience, then try pulling out the update by going through manual software update check by going through Settings. Make sure that you are connected to WiFi and backup important data that is present on your internal storage.