If you ever faced user chat or people who can join in one of chat room of yahoo messenger with 2 or 3 or more ID, and in fact, they also can type with all of those ID or username, you had been seeing the person who use Multi ID. Multi ID is a kind of activity that use 2 or more ID in Yahoo Messenger or others messenger service at once. That Means Multi ID or Multiple ID will makes the user can join yahoo messenger with multiple ID that they had. Of course, they can join chat room of yahoo messenger with all of their ID that been log in. They can join in one chat room with 3 ID, 4 ID or even more. It’s unlimited!