Well, I haven't played around with hacking my iPhone in awhile, but I noticed the other day that my MMS features were gone. I don't know when it happened, or why, so I set about trying to correct it.

I tried all kinds of methods online, but none of them work. Until I found this method that enables MMS, tethering, and all Bluetooth profiles, even on your 2G iPhone OS 3.1.2, which is what I have!

http://modmyi.com/forums/t-mobile/656651-t-mobile-usa-carrier-bundles-bluetooth-data-internet-mms-tethering-2g-3g-3gs.html

It works, and that's great! Now I'm MMSing up a storm, and playing around listening to music in my A2DP headphones! Woohoo!