iPhone 4 IMEI code service help?

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hey! i have tmobile and i bought this iphone off ebay. i recently got it factory unlocked through an IMEI code thing on ebay (for like $20) because i was getting this 'no service' problem. i did some research (and correct me if im wrong) i found out that apple doesnt allow unlocks that arent factory (i think? idk). so the IMEI guy did his part and i plugged it into itunes, restore/backed it up, and it said my phone was unlocked! i was super excited cause i saw it was searching for a signal. but it just went back to saying no service. im soo desperate cause i dont have any other phone! what do you think is wrong, something i did? maybe the code service? the antenna? HELP