Will Apple still help me with my iphone? 10 points! :)?

I have an unlocked iPhone 3g that I'm using on T-mobile. With t-mobile, you do not have MMS by default and you have to go into the phone and turn on something to allow MMS to send and come through. I'm not sure. If I go to the Apple store and ask if they can help me try to get MMS, will they not help me because I'm using the iPhone on T-mobile? I really want to get this phone a try but don't see the point because I'm not getting the full potential from it. Thanks!