MMS is not just a "trigger pull away".
Because of Apple, or more importantly Steve Job's hate for MMS, AT&T had to configure iPhone accounts to specifically not be able to use MMS.
Now AT&T has to go back and convert all 3G and 3G S accounts to enable it while still maintaining the block on 1st gen iPhones.
This is no small task.
And as for the comment about the iPhone keeping AT&T afloat... that's laughable at best.
It's profitable, but hardly their bread and butter.
According to their 2008 annual report (2009 number not available yet), AT&T wireless division as a whole only accounted for $44 million (39%) of the $124 million in earned revenue (after operating expenses) for 2008.
Anyone who thinks AT&T is making money off the iPhone is dead wrong.
To quote from their
2008 annual report:
They are still loosing money on handset sales.
They don't break down revenue/costs by handset, so you will not get iPhone specific numbers out of the data.