Will iPhone 3G still work on AT&T networks?

Thanks for linking to that AT&T page! Very helpful.

I will add that, even if you have an iPhone that will be compatible after the AT&T 3G shutdown, you should check your Voice & Data cellular settings to make sure that you have selected 4G/LTE (or 5G on compatible models) there.

AT&T is changing to VoLTE as the only supported voice protocol after the switch. They have started that move already; if you go to Settings/Cellular you will not see any options to select a network.

That is true. Only the iPhone 6 and newer will continue to work. See:

https://www.att.com/ecms/dam/att/consumer/help/pdf/Devices-Working-on-ATT-Network-After-3G-Goes-Away.pdf