Is there a way that I can find out what carrier my iPhone4 is locked to by using the IMEI number of the handset I bought second hand. I was attempting a restore but it could not complete set up due to SIM card not being compatible.

I recently bought an iPhone 4 from a polish guy and he told me he had bought it for his mum in Poland but because it was too complicated for her to use so decided to sell.I checked it out and it was working normal except I couldn't make any calls in the UK obviously as it was locked to a Polish carrier. On phone details I noticed it said Telenor, but after research I understand there is no Telenor in Poland, rather Orange, T.Mobile are the main carriers.Telenor cover Norway, Sweden and Pakistan.I then decided to restore(stupidly) using a T.Mobile SIM card but unfortunately on the 3rd screen of set up it said SIM card inserted not supported. I then bought a factory restore off eBay where I supplied the phone's IMEI number and then was told this would permanently unlock the phone to any network in the world. however, this hasn't worked even by attempting to restore via iTunes.I am beginning to think I need a remote unlock and restore from apple or find out the original sim that it was locked on to as I can no longer locate the chap I bought the phone from. any help or advice would be greatly appreciated.ta