You can now enable facetime for ipad, but its a 1 way facetime, since iPad does not have a built in camera and mic. This tutorial is not for the faint-hearted though. I've read the site and i can't even understand a thing haha.
Visit 9to5mac for the complete instruction
Via DailyIphoneBlog
Things needed:Conference.framework, IMCore.framework MobilePhone.app, ConferenceRegistrationSettings.bundle, AVFoundation.framework, Celestial.framework, and the UISounds folder all from iPhone 4 or iPod Touch 4 firmware and a Jailbroken iPad running 4.2.1 (works on untethered and tethered)
Visit 9to5mac for the complete instruction
Via DailyIphoneBlog