Check with T-mobile as NOT all texting plans unlimited or not, include MMS (Multi Media Messaging), depends on the text bundle you bought at the time you got it.
A friend has unlimted text messaging on T-Mobile with a package he got over three years ago, that does not include MMS, he pays for each MMS he gets or sends.
I also have an unlimited texting plan that was bundled with unlimited SMS and MMS.
When in doubt, as T-mobile customer service what exactly your plan includes, that way you won't get any nasty surprises at the end of the month when that hot and heavy texting session with that guy in prison, that ended with the two of your sending each other, 500 videos and still pics of you two acting out the Beach Scenes in Beach Blanket Bingo. <wink>