I'm surprised people (especially clients) react better to you not having a cell phone at all than to you not always answering.

I always make sure to disable the auto-away setting in all chat/IM programs so it always shows me as online, and then I explain to everyone that since the program is not smart enough to know for sure that I am available, I prefer to avoid the confusion.

With phones I follow a similar philosophy: I make sure to avoid answering it all the time, I let it run out of battery, or in Silent mode, or I leave it at home, etc. and I'm very vocal about having done so.

I don't know if this makes me antisocial, but it seems to work fairly well in removing other people's expectations (except with my dad heh).