At yesterday’s keynote, Scott Forstall discussed many of the cool features in the upcoming iPhone OS 3.0 update, chief among them support for MMS and data tethering. Support for those 2 technologies, however, are wholly dependant on carrier approval, and noticeably absent from the list of cooperating carriers was AT&T.

AT&T recently stated that MMS support for the iPhone will officially be supported on their network later this summer, even though 29 other carriers worldwide will be adding MMS support immediately. And as for data tethering, you’re almost better off not even asking. AT&T spokesman Mark Siegel recently had this to say about what the future holds for data tethering on the iPhone – “Typically there’s a monthly charge associated with that. We have not announced what that will be.“

Or when it will be for that matter.

Annoyingly, data tethering is already supported by AT&T on a host of other phones, but the iPhone remains the odd man out. Whats confusing about AT&T’s sluggishness on the matter is that people are more than willing to pay a few extra bucks a month for data tethering.

So what’s the hold up? Why is AT&T so willing to act in a way that conjures up so much ill-will towards it?

One possible explanation is that AT&T knows that the iPhone will not be an AT&T exclusive for much longer. While precise details of AT&T’s exclusivity contract remain unknown, it is widely believed that it is set to expire at the end of 2009, opening up the possibility of the iPhone hitting other networks such as Verizon in 2010.

If AT&T knows that there’s nothing it can do to keep Apple away from other carriers, then perhaps it has no incentive to do anything to keep iPhone customers happy. Perhaps it’d rather not have iPhone users using up their bandwidth with MMS videos and data tethering. Perhaps its simply trying to make as much money as it can while keeping bandwidth usage as low as possible before the iPhone moves on to greener pastures in just a few months.

Or maybe AT&T is just incompetent and short-sighted. Take your pick.