atrix4g frm at&t on str talk ...no data need help

ok jus got a atrix and put my straight talk card in there and the phone service is fine im actually getting H+ but i cant get any data out of it. I have check re-checked....re-re-re-checked the settings and it looks right but i sitll cant get a data connection unless im on wifi ,but when i turn wifi off im dead in the water. i can make and recieve text an calls even mms but no internet?

i really like the phone but i need the data portion to work as well!!! PLZ PLZ PLZ help if u can thanks