This is extremely useful function, and I was wondering if anyone has ever seen this in any other phone that's not Blackberry.
Answer:
iOS and android both can do this with many but not all types of email accounts. exchange and activesync accounts have this functionality on both of those OS.
Oddly enough, you have to BES ob BB to get this support. BIS doesnt support it. Many BB owners cant do this either. Its a drawback for many.