Other IM programs don't require that--users of AOL Instant Messenger, for instance, might have a totally different IM name than their e-mail address, or might not even have an AOL account at all.

FORBES

Although many observers predict that AOL would try to bring the ICQ users onto the IM platform, a company spokeswoman acknowledged that the two sets of users are very different and said the company does not plan to force one group to migrate from one system to the other.

CNN: AOL tests linking of instant messenger services