A friendly reminder to anyone in the US that uses Verizon (and possibly T-Mobile) you will need to flash LOS15.1 for your phone to work on the network starting on 1/1/2021.
You need IMS (VoLTE), which LOS15.1 is the last version to support this, for your phone to work as 3G will be shut down on the network(s). There is internal documentation that T-Mobile is shutting down their 3G network on 1/1/2021 but nothing has been released publicly. For those on AT&T they will shut down their 3G network 1/1/2022.
Happy Holidays everybody!!