Question for former US Cellular customers who stayed with T mobile

I live in some rough-ish country and T-mobile apparently dropped some of the USCellular towers and the phone is on AT&T probably a third of the time now. The overall service is not at USC levels, but I am pretty sure this is as good as it's going to get. The problem is when the phone is connected to AT&T I can't access voicemail. I go a quarter mile away from home and the phone returns to T-mobile where it works normally. I suspect this is a phone issue- according to the AT&T website my model of Kyocera phone is not compatible with their network, but I am wondering if anyone else is having similar issues.