Just a couple things to consider first. One... there isn't an Untethered JB for iOS 5.1 yet but, your friend can have a Tethered JB until then. Second, is your friend relying on any type of an Unlock since sitting at 4.2.1?my friends have an iPhone 3gs jailbreaken ios 4.2.1 . he interested to ios 5.1 . he want to upgrade his iphone 3gs ios 4.2.1 to ios 5.1 . can you give some advise to this post ? should my friends upgrade or not ? feel free to reply this post .