We try to e-mail responses to phone questions. It's very convenient to do that with the web - you can copy text and include URLs. I agree that e-mailing is problematic. It's related to library anxiety. That's why it's so important to have pathfinders, etc.
Instruction is proactive versus reference which is reactive.
We need to provide and promote these mechanisms. The University of Michigan does with all camp us libraries. The North Suburban system in Illinois has one place for homework help by phone or e- mail. People don't know how to use pathfinders, etc. You've got people asking questions at times when no one is in the library.