Diablo III will be almost region free to allow "global play" with anyone in the world.
Diablo III's servers have been split up into three regions. Americas (which also includes Australia and New Zealand), Asia and Europe; however, they will be region free, allowing players to use any server.
With that in mind, they won't be entirely region free. You will need a new friends list, character and items for each server.
Real world money auctions will also limit players to their own region. Normal in-game gold, however, can be used by anyone.
By Ben Salter