At least your heard from open Battle.net.
" What is an Open Character?
Open Characters are stored locally on your own computer and, while you can set up games and chat over Battle.net, you cannot play these characters on a Diablo II Realm. In an Open Game, one player’s computer is the game server, while the other players connect to it. Since Blizzard cannot be responsible for the locally stored characters, or the servers upon which the games are played, Open Games are more vulnerable than Realm Games to certain forms of manipulation and abuses by other players. The big advantage of Open Games, however, is that you can bring your Single-Player Characters onto Battle.net. You can play with your friends over Battle.net and then continue playing that character in Single Player as often as you want."
Looks like i find another. The list of D2 experts here are getting bigger and bigger.
You can have fun on open Battle.net any time