I am planning on unlocking my iphone to sell on ebay, but all I have at hands reach are AT&T cell phones, is there any way I can see if it will work on other GSM carriers without having the actual sim card?
If you use PWNAGE, go to bootneuter and see if basband is unlocked. If it is you should be fine. Although, I was in the same position as you are now. My first unlock and I only had AT&T. Ended up getting my friends sim and it worked perfect.
Make sure all sms, data, email, maps, youtube, etc all work and you should be fine.