A new update has started hitting the Verizon-exclusive Droid Turbo 2. Arriving as software version 24.31.22, the update includes the WiFi Calling feature as well as latest security fixes. As usual, there are some bug fixes included as well. As is usually the case with OTA roll-outs, it may take some time for the update to hit your device. Meanwhile, if you feel impatient, you can also manually check for it by heading to your handset's Settings menu. Source
Source: http://www.gsmarena.com/update_brings_wifi_calling_to_droid_turbo_2-news-20820.php
