I train my receptionist. I give her a list of the vendors we deal with(Dell, Toshiba Business Solutions, etc...) She orders toner for the copiers anyway, so she knows not to take any of those phone calls. Anyone else, especially when someone says, "My call just dropped while I was talking to your IT guy. Can you put me back in touch with him?", she calls me first and asks if I was just talking to someone. I say "nope," and she just handles it.
I feel really bad for any IT person that actually has to deal with these issues. It's the responsibility of the receptionist, not you, to filter phone calls.
