Is there some way to break up user keys more granually, so that you can issue subkeys to other things to act on your behalf? E.g. having a separate read key and write key, or a write key with instructions for clients to ignore posts to all but one channel, etc, alongside a channel dedicated to key revocations. That way you could share an "API key" with a third party system.
It's really easy to send SMS/MMS messages via Twilio's api. There is a Node.js library too.