Once AT&T 3G shuts down, chances are it won't be able to connect to the network due to how it logs on. While the AT&T site[0] says "will decommission our 3G networks on February 22, 2022", but it's actually been pretty slow with 3G still lingering in many places and others getting it turned off around the time they're working on 5G deployments utilizing the now-free spectrum[1,2]. They probably could've fixed this by updating V10 with only the modem changes but they want people on V11 more.