Being the most popular tablet and all, the iPad has been the target of quite a few tweaks, including at least two that convert it into a phone. The latest one? Multiple user support via the Cydia mod iUsers. Via a log-in button on the iPad's lock screen, iUsers allows iPad owners to create multiple users accounts, allowing separate users to have their own preferences and data. Unfortunately, that separation does not yet extent to music, videos, and apps - at least not yet.
Of course, this is the exact kind of functionality most would love Apple to have included in the iPad to begin with. Then again, considering that the iPad is "post PC" and all, maybe Apple isn't so keen on replicating user switching on its tablet. Either way, add iUsers to the expanding list of reasons to jailbreak your iPad.