AT&T Activates MMS Functionality for U.S. iPhone Users. Welcome to the world of MMS my American friends. Course, up here in Canada we've had this since the original iPhone OS 3.0 release. I've used the functionality exactly twice, once to see if it worked and the second when I received an MMS of what looked like someone's butt from a friend testing to see if their MMS worked. Hope ya'll use it more than I do.