I recently purchased a used unlocked 3gs in the US and came back today to Prague. I hooked up the phone to itunes and it says I need to restore and upgrade. I have no idea what OS it is running, not given by buyer and didn't know I needed to ask. the iphone screen is on the restore screen, and have no idea if i should proceed with restore and upgrade or not. I think it will upgrade and then won't be unlocked afterwards. I have been reading posts for an hour, and not sure what to do. I'm good at following instructions, but a lot of what i am reading, i have never dealt with before.