I've spoken to AT&T several times about this and have pieced together that the feature we're missing, for unlocked phones, is enabling the HD Voice feature on the line. It's what allows services like calls over WiFi, Advanced\Enhanced SMS\MMS, AT&T Mobile Security and AT&T Call Protect. It does get immediately turned off once it recognizes that you're phone isn't once if theirs. Apparently the S10' have recently been added to the "approved list" of unlocked phones. Hoping they allow the Note 10 Plus soon! I've tried tricking the auto-provisioning by putting the SIM card into an AT&T Note 8 and having them enable HD Voice. Then, putting the SIM into my unlocked Note 10 Plus. It immediately removes HD Voice off my line at that point. They don't have the option at all while the SIM is in the unlocked Note 10 Plus.
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