Windows 10 Mobile won't ring on AT&T 3G cell tower

[Windows Central Question]

After two days of troubleshooting with AT&T, we have figured out that Due to AT&T shutting off all 2G, if you are connected to a tower that only has 3G, Windows 10 phones will not ring on an incoming call and take a long time to connect an out going call. Text works fine. Comically, if you are in a call while connected to a 3G cell tower, a new call will ring your phone. I tested with a Lumia 950 and 950 XL.