This video tutorial shows how to get MMS on iPhone 3G for Tmobile on 3.0 or 3.0.1. Not that this works on T-Mobile's Network ONLY
To add MMS go to:
Settings-General-Network-Cellular Data Network
Add this in MMS field:
Username: *leave blank*
Password: *leave blank*
MMS Proxy: 184.108.40.206:8080
MMS Max Message Size: *leave blank*
MMS UA Prof URL: *leave blank*
Then reboot your iPhone.
Then the picture icon will show up in the Messages App.
There is no additional charge for MMS on T-Mobile's Network. Same price as sending a normal text.