Personally I don't think I'd care if I had a title and it wasn't used (but as I don't have one I would say that wouldn't I...).

Professionally however I'm head of Customer Service for a multi-national company and one of the first things we teach new starters is how to address clients by the correct title. Fail to address a German Dr (academic as well as medical) properly and you will know about it pretty sharpish. The question "who am I speaking to" or "can I take your name" is perfect as you can take your cue from the client. Most of our clients are lawyers and we end up using first names for most British clients, Mr/mrs in the US and exchanging grunts with French people