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Provider doesn't matter. I'm paying $6/mo for a Snikket instance, and $5/mo for a phone number from jmp.chat.
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You can use any of them, Jabber, conversations, Snikket, cheogram, Prosody, etc. Xmpp works regardless of host. You could host your own and so task to people from other servers, it's almost like an email address or how Lemmy instances can see and talk.
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Correct, you don't have to host your own server, but like I said I do for friends and family.
You could test it out if you like, most servers have free sign ups. Cheogram I think lists several that're open too. You can text other xmpp users as well as SMS-though be mindful no encryption is used for SMS. Just TLS but that's obv not e2ee.