Despite the fact that the Wii U Gamepad has a perfectly good microphone, to enable voice chat Nintendo have said you will need a licensed headset that plugs into the Gamepad's microphone port.
So far just Venom have confirmed that they are offering a licensed stereo headset for £24.99. Turtle Beach and Mad Catz are sure to follow
Currently the only games with confirmed voice chat support are:- Assassin?s Creed III, Mass Effect 3 and Call of Duty: Black Ops II.
Wireless Wii U headsets
As yet there is no news of a wireless Wii U headset. Technically there should be nothing to prevent one being manufactured, as the Wii U gamepad has Bluetooth built in.