Blizzard should launch their own IM service; The Battle.net 2.0 Messenger

This's something else I posted years before SC2's announcement, and now that they've introduced a single-login system and global accounts for the new Battle.net, it’d be a perfect time to have a Battle.net Instant-Messaging client;

The Battle.net Messenger (BNM? BM? BMS?)
For the next-generation of Blizzard games, like StarCraft II and Diablo III, this'll allow you to;

• see and chat with all your Battle.net friends, whether they are playing a game or not.
  If they are in SC2 or D3 for example, they would get your messages in-game, unless they choose not to be disturbed.
  and if they're not logged on to a game, the Messenger would act like any other IM client, i.e. Live Messenger or AIM.

• see all available custom games in a convenient list, and join them with simply a click (or two.)
  For example, even if you don't have the SC2 executable already running, the Battle.net Messenger will launch it and send you straight to the lobby of the custom game you chose, skipping any preceding UI or cinematic whatsoever.

Also, maybe through integration with the Messenger, a Blizzard game, say SC2, would let you stay in touch with players on other games, like D3.
This could obviously be used for many other things, including an always-active venue on the users' end for Blizzard to place advertisements on and provide announcements through. :)