If you're waiting for a jailbreak before updating to iOS 4.2.1, you might be happy to know that redsn0w 0.9.6b4 will do the trick. It uses the Limera1n exploit that worked with iOS 4.1, however this is currently a "tethered" jailbreak. In other words, once you jailbreak using the current method, if you ever need to reboot your iPad, fourth-gen and third-gen iPod touch, iPhone 3GS (later models) or iPhone 4, you must have the device connected to your computer and use redsn0w to do the reboot, otherwise the phone simply won't boot up. Definitely not something we'd feel comfortable doing with our main device, but hey, we know there are many out there who are more daring than we are. If that's you, go for it and let us know how it went!
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In our opinion, the best reason to subscribe to MobileMe has been the Find My iPhone service, a feature that allows anyone to pinpoint on a map where their iPhone, iPod touch, or iPad are located, in case they can't find them. You can also send a message to your device, play a sound, remote lock it, or even remote wipe. Today, in a surprising move, Apple decided to unbundle the service from MobileMe and offer it for free for the latest generation of iOS devices. So if you have an iPhone 4, fourth-generation iPod Touch, or an iPad running iOS 4.2.1 or later, you're in!