Because SMTP is a fully-federated protocol whose main feature (text messages) overlaps with XMPP, a fully-bidirectional no-registration-required gateway should be possible.
If this gateway were connected to a Cheogram JID for 1:1 routing to a DID with some provider, then bidirectional SMS-to-SMTP is the result in a fairly straightforward manner.
Because SMTP is a fully-federated protocol whose main feature (text messages) overlaps with XMPP, a fully-bidirectional no-registration-required gateway should be possible.
If this gateway were connected to a Cheogram JID for 1:1 routing to a DID with some provider, then bidirectional SMS-to-SMTP is the result in a fairly straightforward manner.