(to) Instant Migrate
Meaning to log off MSN, AIM, or any other IM software without saying goodbye to the people you are talking to.
Someone who does this a lot is known as an Instant Migrator.
Person #1: I cant believe you Instant Migrated from our conversation last night.
Person #2: And...
Person #1: You do it all the time you f**cking instant migrator. It's really annoying.