try to reset all the settings, and you'd better remove that's useless apps or settings.
BTW, this topics I stumbled upon might can do some help for iPhone 4 users or upgrade iPhone to iOS4.
"Copy iPhone 4 iMovies To iPad", "iOS 4 Upgrade Guide: Install iOS 4 on Your iPhone", "Handbrake Presets for iPhone 4 and iPad", "The differences between the iPhone 4 and the iPhone 3GS" all located in iFunia: iFunia | iPhone Column
of course, if you have any video conversion problems, you can get ifuna to have a try.(now Im using its free YouTube downloader, very nice.)