Customers with Sprint 3G dependent devices will be receiving a letter from T-Mobile stating on January 1, 2022, Sprint’s older 3G (CDMA) network will be retired. If they are still using a device that is dependent on Sprint’s 3G network or that does not support VoLTE, they will need to upgrade to a more modern device no later than the end of 2021 to continue getting service, including the ability to make 911 calls depending on their location.
For additional information on this topic, check out: https://www.t-mobile.com/support/coverage/t-mobile-network-evolution