Check out this video to learn how to get MMS on iPhone 3G for T-Mobile on 3.0 firmware.
This works on T-Mobile's Network only!
Add these to MMS Settings in: Settings-General-Network-Cellular Data Network.
Add this in MMS field:
Username: leave blank
Password: leave blank
MMS Proxy: 22.214.171.124:8080
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.
This allows you to send pictures, video and audio messages for the same price as a text.
There is no additional charge for MMS on T-Mobile's Network. Same price as sending a text.