Preview at WWDC likely in June, followed by September launch.
Rumors of iPhone OS 3.1 Appearing Next Week Alongside MMS from AT&T Based on Questionable Sources
Many sites are pointing to Know Your Mobile as a source for the rumor. That story, however, appears to be a slight embellishment of claims made by FSMdotCOM last week. FSMdotCOM's report, in turn, quotes a ModMyi user who noticed portions of MMS functionality in the iPhone OS 3.1 beta and who reportedly received word from an AT&T representative that MMS would be enabled by the end of the month in backing up a previous FSMdotCOM report from early August simply claiming that MMS functionality would be coming "later this summer" after the launch of iPhone OS 3.1.
Further confusing the issue is that the follow-up FSMdotCOM report citing the ModMyi claim was made in late August, and the end of the month has come and gone with no sign of MMS on AT&T. Other sites, however, didn't pick up on the story until September, and some have misinterpreted the report to be claiming an end-of-September timeframe.
In essence, all of the claims seem to stem from the original FSMdotCOM report from early August that simply noted what was already known or reasonably surmised.
The information i just got from my AT&T ninja , seems to be the same as "later this summer". He told me that AT&T will enable MMS for its users once the new iPhone firmware 3.1 will be released . Released date for the new firmware is not certain, all we know is that it will be released towards the end of August or early September.This is not to discount the possibility of iPhone OS 3.1 being launched next week with MMS from AT&T coming along for the ride, as it is a reasonable guess based on Apple's introduction of iPhone OS 2.1 at last year's event and MMS being turned on by default in iPhone OS 3.1 betas, but claims of anything more than speculation appear to based on little solid information at this time.