I am having similar problems as the original poster. My phone is an Iphone 3g (8gb) jailbroken with firmware 4.2.1 and basband 06.15.00. When ever I go to the the apple apps store on the phone and try to download any app (free or paid for,) it just goes back to the springboard. Is this cause I have a jailbroken phone and need to un-jailbreak it? I don't really want to un-jailbreak for fear of losing the unlock. Yes I did jailbreak it myself. Please, any help would be appreciated! Have only had the phone about a week and its just a telephone at the moment!