I'm having severe issues going between towers. Even Downtown Seattle I walked out of a building and it said I had 4G. Missed calls that went straight to voicemail, then I receive the notification I have a voicemail some time later.
I called in and certain areas switch over to the Edge Network. But I did a test with 3 family iPhone 5's. Calling them from a land line, only 1 of the three rang. The rest went straight to voice mail. I continued randomly test calling and it varied. But it was obvious not all calls were making it to the phones showing 3 bars of service.
They instructed me to turn off Settings->Cellular->Enable LTE to off. Got mixed results off doing that.
I continually just reboot my phone or flip it to airplane mode, then back off to get it to jog the network. I've also reset network settings a number of times.
I never had this issue before with my 3G or 4S phones.