I got a reply and I understand that a GSM-compatible phone will work. However, my question was in regard to 3G versus 4G, 5G phones. ATT is getting out of the 3G network. So, a phone that is 3G GSM may not work with the carrier network, am I right? The phone needs to be upgraded to a 4G GSM? If I don't upgrade the phone, will it work if I use the Freedompop Freemium Sim (instead of ATT's Sim card). It is one of those ATT's 'Go Phone' sold at retail stores a few years ago. The phone model is the ZTE Z223.
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