AT&T has released a new over-the-air software update for the Galaxy S4 Mini which introduces support for voice-over-LTE calls, as noted by Android Central. The update also includes the ability to dial 911 without a SIM card in the phone.
VOLTE Software Update Includes
- VoLTE inter-op call hold
- SIM less 911 Dialing update
- ISIM SQN re-sync for VoLTE reregistration
- v4v6 for IMS PDN while roaming
You can grab the update for yourself by opening the Software Update screen in the Settings app.