Network not available for voice calls

Hello,

I have AT&T prepaid service. I've had it for a long time with no problems. I've swapped my sim card to a couple of different phones and can't make calls on any of them. They will send text messages OK (wifi and bluetooth is off). When I try to make a call the phones will beep after a few seconds and a message pops up that says "Network is not available for voice calls". or "Mobile network is not available". It shows it is receiving a 4G signal. Everything works good except voice calls. My phone was underwater overnight a few days ago. I removed the sim card and trashed that phone. Have tried the sim on a couple of different phones with the same results.