> That lowest common denominator will be probably being able to send text messages. Maybe a little more.
It was my understanding that we already have a (fairly old) standard that does just that, which also currently works as a lowest common denominator for texting between at least android and iOS.
There’s a telecom protocol tied to your carrier and phone number that predates both android and iOS, but not a (free to use, free to implement) internet protocol. (EDIT: unless you are talking about email)
