IGN posed a question to Perrin Kaplan of Nintendo America about whether the Wii would follow in the Nintendo DS' footsteps and be region-free.

We will share a lot of ways people can play globally, regionally, without boundaries. You're right that the region-free approach has proved to be a successful and attractive feature for Nintendo Wi-Fi Connection on Nintendo DS -- we have even blown the doors off our own anticipated numbers! Cost, ease-of-use and player privacy are the three things that were a focus for us with Nintendo Wi-Fi Connection. Those priorities also will apply to the Wii system.

Not a confirmation, but it certainly seems set to be region-free.