This will allow you to have MMS capabilties (sending and receiving) on your idevices and on all unlocked devices even 4S (unlocked with UltraSnow + Fixer or factory unlocked) exceptional those using unlock with Gevey sim.
First you need to install CommCenter patch:
backspace.jp Cydia Repository
in your cydia sources and install CommCenter Patch
After that you need to install T-Mobile USA carrier bundle ios 5.1.1 for your iphone, for more information on how to install carrier bundle on your iphone please refer to this thread : T-Mobile MMS-USA Patching CommCenter (Does not work with Gevey users) - SiNfuL iPhone
Download T-Mobile USA carrier bundle for ios 5.1.1 : IPCC file