You may have no noticed, but AT&T shut down its 2G Network sixteen days ago on January 1st, 2017. This shutdown did not come as a surprise after all the wireless carrier announced its intent to remove 2G around four years ago. This ensured that any customers still on the network could upgrade to 3G or even 4G LTE devices.
A big device that used 2G Networks was the original iPhone, which turned ten last week. While not that many people still used this device, it no longer has a network to live on, at least for cellular service. After all the original iPhone did have WiFi onboard, so it can still connect to wireless networks. AT&T is not shutting down the 2G Network due to age, but rather to free up network space for future technologies.
And yes a big reason is to enhance its current 4G LTE network, as well to plan for a 5G Network rollout in the coming years. Over the coming months, AT&T will repurpose a vast majority of the network and continue to build out 4G LTE across the nation. If you still have a 2G device on AT&T, you can reach out to the carrier to move to 4G LTE.