I added this link to the Cydia sources section http://beta.leimobile.com/repo after adding it go in it and look for Tmobile 4.0 MMS Fix, and install. After it finishes installing hit the reboot button. Thats it, from there it should be working. Have someone send u a picture message to check it out... It worked for me and I have the iPhone 3g 4.0

I hope this works for you guys...