Trouble activating iphone 4

Recently bought my first iphone. I had no idea it needed a certain carriers sim to active it. I have no access to said carriers sim as it is not sold in my country and I have no way to get hold of one. Is there any way around this?

I got a IMEI check to see if it locked to one carrier and it isn't I'm just not able to activate it. Very frustrating.

Any ideas are much appreciated.

Cheers, Callum.