NEED HELP WITH MY SONY ERICSSON W850I PLLLLZ!!!

I have this Sony ericsson w850i on Orange. Basicly I can receive text msgs but when I try 2 reply, I only get the options of picture msg and voice msg but not text. Is there lyk a setting I need or sumthing. Btw I tried ma m8s orange sim and his one works fine, it can send texts. Btw I can call with no problems