The MMS on/off on 3.0 seems to be missing from my phone. I'm on AT&T, is that why it isn't there?
If you want it back and don't mind jumping through some hoops, took me about 20 minutes total, here are some instructions.
Ok this is assuming you are using the official iTunes 8.2 and windows. I think a mac would be similar but don't have one so can't be sure.
1) install GM seed on iPhone.
2) restore from back up or set up as new
3) uninstall official 8.2
4) uninstall apple mobile device support
5) install iTunes 8.2 tha shipped with beta 4
MEGAUPLOAD - The leading online storage and file delivery service * * **
itunessetupwindows.zip
6) move your iTunes library file (itunes.itl) to a different location if it was updated with the official 8.2
7) open iTunes
8) update your ipcc file with this one
MEGAUPLOAD - The leading online storage and file delivery service
Update the same way you do the ipsw just change the file type to ipcc and navigate to the file
9) restart your phone and the mms options should be there
10) uninstall beta 4 iTunes 8.2
11) uninstall apple mobile device support
12) reinstall official 8.2 and replace the empty iTunes.itl with the one you moved. You should be good to go, provided your account is provisioned for mms.