I'm hoping this can be done, I'm not really a fan of swirly MMS, it can be too stubborn. I'm sure someone will be able to get a work around, it could be as simple as some code missing in the firmware(hopefully).
Since SwirlyMMS can do MMS on the iPhone 2G, and BiteSMS is working on MMS on the iPhone 2G - I am pretty sure that someone could figure out how to turn on the "official" Apple MMS on the iPhone 2G.
I would bet that it involves replacing the Messaging application in the 2G firmware with the Messaging application in the 3G firmware, and then maybe a tweak or two.
Its not as simple as you think.
MMS is not available/included in the 3.0 software for the 2G iphone so making it work with the 3G install file is not just a tweak or two.
Alot easier to just use swirrlymms.
I would bet that it involves replacing the Messaging application in the 2G firmware with the Messaging application in the 3G firmware, and then maybe a tweak or two.