I have a blackberry from t-mobile but I have cingular as my service provider. Is there any way I can get the unlock code for it?

Yes, TMo might give it to you for free if you were a customer of theirs.

Otherwise, you will need to purchase an unlock code from a vendor, such as:

HorizonWirelessOnline.com - Horizon Wireless, The World’s Cellular Repair Center ß

^^ good and reputable vendor...