Nintendo Network Premium is included with the purchase of the black Wii U Premium bundle that comes with the more expensive 32GB console. It is currently priced at 31,500 yen ($405) and comes with the black Wii U, a Wii U gamepad charging dock and stand, a Wii U console stand.
Nintendo initially said that the Nintendo Network online service would be free but couldn't guarantee that it would always be that way. It sounds initially like they are going with something similar to Playstation Plus in the form of Nintendo Network Premium but it's actually more of a rewards program.
Games purchased online via Nintendo Network Premium gives back 10% of the purchase price in Premium points that can then be exchanged in increments of 500 for Nintendo Points that can then be used to purchase other games and DLC.
The service will only be offered through 2014 but it is currently unknown if those that purchase the white Basic Wii U package will be able to buy a Nintendo Network Premium subscription.