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While I too find voice mail irritating,
I find IM to be equally annoying. I can talk a lot faster than I can type, and the lack of a spell checker annoys me to no end. If I need an immediate answer, I reach for the phone first. If it isn't urgent or I don't get an answer, I send an e-mail. I'll respond if a co-worker initiates an IM conversation, but I don't see any advantages in my situation.