Apple’s big new system update, the iOS 4, arrives today for the soon to be released iPhone 4, the 3GS, and 3G. Just in case you didn’t know, the iOS 4 brings long-awaited multitasking to the iPhone, along with folder support, the iBooks app, and an improved Mail. Sorry 3G users — you’ll get everything but the multitasking, and any phone models before that are straight outta luck. You’ll need iTunes 9.2 to update, which is available via Software Update on OSX or Apple’s site. You can find detailed info on all of iOS 4′s new features right here.