From AT&T directly:

AT&T GSM 850/1900MHz 2G network shutdown

“To help support increasing mobile Internet usage and continue to provide you with a great customer experience, we started to discontinue service on our 2G wireless network as of December 31, 2016.

AT&T wireless customers attempting to use this network after the shutdown will be unable to:

  • Make or receive calls, including emergency calls.
  • Send or receive text messages.
  • Use data services.

We’ve provided advance notice and numerous communications about our 2G migration to provide a long lead time for upgrading to a 3G or 4G LTE device.  We’ve tried to make the transition as easy as possible.  We’ll continue to work closely with all customers to make the transition to newer technologies.

Device Requirements Post-2G Shutdown
After December 31, 2016, the minimum requirement needed to operate on AT&T’s network is 3G; WCDMA (UMTS) HSPA 850/1900 Mhz Band 2 and Band 5.

Note: Devices that do not support these specifications may also be impacted by the 2G shutdown and may need to be upgraded.

What to do if you still have a 2G device

You should have received notifications from AT&T regarding a network shutdown if we identified a device on your account as using our 2G network.  If you haven’t upgraded or activated your new device yet, please take the following steps:”