Is there an S21 model that will work on both CDMA and GSM?

I saw in one of your other posts that you were on Verizon at the time. If that's still true, then I wouldn't worry. Verizon is getting ready to kill off their CDMA network, and their VoLTE network is nationwide. As long as the phone is compatible with Verizon's 4G bands and has HD calling, you should be fine.
 

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