If you recently completed your activation, did you insert your SIM card in your phone and turn your device completely off and back on? If so, allow your phone about 15 minutes to fully activate and connect to your surrounding towers.
If your phone prompts you to attempt a carrier update, please do so to allow your SIM to fully program. Also check your coverage zone if you experience issues while making or receiving calls.
If you find you are in a spot of service that should not drop your calls, let us know and we will help you troubleshoot any issues!