Cant send MMS on Straight Talk on my iphone 4S. Help!

I recently switched from AT&T to straight talk because i can no longer afford their packages. Straight talk is much cheaper but my only problem is it wont let me send pictures or anything through text messages. I heard i can adjust stuff to make it work but idk. Please Help

Is your iPhone unlocked or jailbroken? If not it wont get data on Straight Talk

I have the same issue but mine is unlocked and it just has an e up at the top and jumps back to at&t when im not in wifi

I can send some text messages but not others. Anyone have any ideas? I am using an Iphone 4s. Everything else seems to be working.