Hi everyone. I'm trying to find out if iPhone 3GS with 4.1 operating system is possible to jailbreak? I thought it was. I watched a bunch of videos on youtube and did plenty or research online and my research led me to believe that I can jailbreak my iPhone 3GS with this software: http://www.greenpois0n.com/ I did that and unlocked the jailbroken iPhone within Cydia in and ultrasn0w. It seemed all done but I had an interested buyer and he took out the sim card and added a T-Mobile sim card and he mentioned it was not unlocked. Any ideas as to what could have happened? The phone indicated that ultrasn0w was installed. Did he not know what he was doing? Just needing to get this resolved so I could move on. Any help would be appreciated.