Thanks! Very interesting. This basically makes international SMS free instead of the typical 50c. Nice shot taken by MetroPCS at the big guys.
Interoperability is one of the few advantages carriers have. If Joyn is built-in like it is in Europe, users won't need to coordinate with the other end to use the same app; can just use the phone number for rich communications (messaging, voice, video, files, etc) over data.