this is just like the other forums and threads have. just i got this one to work
1)go to cydia.
2)go to manage-sources-edit-add and add the repo Smart-Mobile.com
3)i rebooted my phone.
4)after the reboot i went back to cydia and installed "activate mms 2g (3.1.3)"
5)after install it will prompt you to reboot. after that reboot go back to cydia and REINSTALL "ACTIVATE MMS 2G (3.1.3)" ABOUT 4 OR 5 TIMES!
6)after rebooting go to settings-general-network-cellular data network and add these settings
mms proxy: 188.8.131.52:8080
mms max message size: 60000
mms us prof url: http://www.apple.com/mms/uaprof.rdf
7)reboot. go to settings-message- and it should have a mms setting in message.
i reinstalled "activate mms 2g (3.1.3) about 5 times. i didnt install nothing else. just reinstall right after each other.
it should work. working fine for mine. let me know if it doesnt.
if you are having trouble recieving mms' install tmobile ios fix from pushfix
(from a member - Snowcolt)
I'm not sure why he had to reinstall it, but maybe that's what you need to get it working. I also know there is a t-mobile fix from X-sellize you might want if it's not working, and also the Push fix repo t-mobile fix as mentioned.