If you have an old 3G phone you will have to upgrade. If you have a 4G LTE phone it will continue to have service for another decade. If you haven't heard from your phone service that your phone will be kaput then it won't be...

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What cell phones will not work in 2022?
Some tracfones, flip phones, Jitterbugs and even older-style smartphones will no longer be able to make calls once the networks are taken down. Most of these phones, which are sometimes called “third generation” phones were launched nearly 20 years ago and will no longer work with most of the carriers in 2022


Article from last year...

https://www.washingtonpost.com/technology/2021/09/30/3g-networks-ending/