Is anyone aware of an IM client which is explicitly asychronous in the way that SMS is? i.e. one where instead of messages demanding instant replies, they "pile up" and await your attention. I'd be interested to see how this changed messaging behaviour - personally I think I'd find it more polite than an application which seems explicitly designed to interrupt me when I'm working.

(which is not to say I can't see the value of IM, or don't use it)

I think this would be purely a question of a new interface (rather than new protocols): don't pop up a window when a message comes in, just beep and invite me to check it out when I have time. I guess this is a bit like "email with presence" or err "fixed line SMS" ()

Update: hmm, actually there seem to be some settings in MSN Messenger which stop the automatic popping up of Windows; I can't check right now (on the train up to Leeds) but maybe I can munge Messenger into approximating what I'm after...