Unlocked L7, problems with pic and video messages

I just bought an L7 phone that was unlocked. When I tried to send a pic messages or video message it wouldnt go through, then when I sent a pic message from another phone to this cell it wouldnt let it download it said unable to download. I am using tmobile as my service. Is there anything I can do that really the only reason I bought this phone, is there anything at all I can do so I can send a message??? Thanks everyone...