Help with D500C and email setting

Hi everyone...

i'm a noobie here....and i just have a quick question... i bought an unlocked d500c for use with t-mobile.....the problem is...i signed up for internet and picture and video messaging.... the thing is....everytime i send or try.... i get an unknown subscription thingy.... any help would be appreciated.... i don't know what tmobile would say if i called and asked them.....so please please help ^^