Someone correct me if I'm wrong here...
First, I have a question. Did those who were trying to get SwirlyMMS to work experience the same problems, i.e. calling AT&T to provision the account for MMS which would fix Swirly, only to have it unexpectedly turned off later?
If so, I think what is happening is this: Back in the day, once AT&T realized that people were provisioning their iPhones for MMS so they could use Swirly, they started doing blanket sweeps across the network to un-provision iPhones that had allowed MMS, assuming that all of these people had jailbroken their phones anyway.
But now that 3.0 is out, and it's legit to have MMS, AT&T hasn't turned off this blanket sweeping all iPhones on a regular basis to turn off MMS. They will obviously stop this system come summertime when 3.0 is standard.
We are basically suffering the consequences meant for jailbreakers, not beta testers.