It is not yet available in North America, but Japan gets it in a few short days.
Nintendo TVii will be part of the Japanese Wii U's day one update, confirmed Iwata during this mornings Nintendo Direct presentation.
The service, which is currently not available elsewhere, will contain different content than its North American counterpart. Even though the service itself is free, the ability to change channels with Nintendo TVii will cost Japanese gamers 100 yen to unlock.
Nintendo's North American and European Nintendo Direct presentations are scheduled for later today and may or may not contain information for the services worldwide distribution.