officially licensed headsets plugged into the WiiPad's headphone jack, but voice chat will not be standard across all games or even the system itself. Even though the WiiPad has a built-in microphone, it can't be used for voice chat.
Things get a bit more complicated when you enter the Pro Controller into the mix. The Pro Controller doesn't even have a headphone jack, so for a game like Call of Duty: Black Ops 2, players will need to plug their headset into the WiiPad and set it next to them while they play with the Pro Controller.
So far the only games listed to support in-game voice chat are Assassin's Creed 3, Mass Effect 3 and Black Ops 2. Nintendo has yet to announce voice chat support for any further games, never mind detailed plans of the Wii U's online suite.