Yes, tried manually choosing T-Mobile as well as AT&T, and got errors for both not being able to find the network; however, I did not try using TextNow or Fongo, so I might do that next time. Thanks for the suggestion!
I wish I'd found this before buying the $35 addon for US voice, data and SMS. Like the OP said, my Galaxy S10 could only use the data and SMS. No voice. I realize now the Galaxy S10 is not listed on the PM VoLTE list I wonder why PM does not make ...