I am currently running version 3.0.1 (firmware 04.26.08) on an iPhone 3GS. Phone has never been jailbroken. I have remained at 3.0.1 so that I can enable tethering. I am now ready to upgrade to iOS4 but want to leave the possibility of allowing the phone to be jailbroken/unlocked. Is this possible? If so, do I simply use the latest Pwnage tool? Are there any advantages to keeping this firmware (04.26.08) and, if so, is there a way to save the firmware for later restore? I have read where having the latest firmware will have less dropped calls, so I have no problem upgrading, just would like to know what I am losing (resale value, perhaps?).