Full client is release, Test client is open Beta. The Korean server run a rolling test server and client, it gets reset every so often I believe, so the players can prat about with new stuff on there, but better not worry about building up epic loot and such. There are more bugs, but also the latest features. On the Full server, they will get more support for lost items, crashed accounts and so on. They only log hackers and cheats on the Test server, on the full one, they are banned.
Either of those clients will work on most of the servers released here.