I am new here and have no idea what I'm doing. I have an iPhone 3GS (without service) which I only use for wifi use for apps, etc. I own an iPhone 4 now for for my regular useI use it more than my PC. I've been exploring and saw the term (GSM) only. Can someone tell me what this means? I found it while reading about unlocking and jail breaking an iPhone 4 (I also read that I can't do that with my firmware?I think).