I'm interested in buying a second hand iPhone for use on Cincinnati Bell Wireless. I understand that I will need to unlock/jailbreak/etc the phone for use on the network. I seem to be having a difficult time finding concise answers as to WHICH iPhone models I can be looking for on the used market. I don't want to get stuck with a model that is TOO recent and can't be unlocked or upgraded/downgraded. What model/OS is the best bet for the 'best' iPhone I can still use on an outside carrier? Can the pre-3g iPhones be upgraded to more current OSs if I decide to save some $$$? Is there an UP TO DATE, comprehensive guide to this process anywhere? I'd be very appreciative of any info or advice. Thanks!