I'm not sure and someone with more knowledge than I could set us straight, but I think all IM's, emails, TM's, etc. are archived on ISP and related servers for a certain period of time. I think the ISP's release of those messages without an express court order could be against the law, but since the Bush Administration has been messing with the privacy act, it's legality may be a non-issue now.
Two thoughts come to mind:
1) NEVER put in unsecured electronic form anything you wouldn't want to be made public.
2) Be careful of what you wish ( ie. internet, phonecall snooping without warrant) - for it might just come true.
Very good advice.