Nokia 7610

I purchased Nokia 7610 last July unbranded and phone worked fine until now. I called Nokia USA and was told that my phone is European version and they wont be able to help me, that sucks . Anyway, to make long story short, my T-mobile sim is not working with my 7610, i can't receive incoming calls and hear this message "The subscriber number you dialed is not available or out of service area...blah blah" 😲 😕

If you've run into this problem and know how to fix, please guide me through. Your help is greatly appreciated. Thanks