How IT are you?
D, keep them on the phone as long as humanly possible and involve as much tedious small talk as you can muster. In between the tedium try and get as may Monty Python quotes in without being obvious. Gauge their own assumed knowledge with near incomprehensible babble about flooded packet gateways, network degradation based on 443htz bleed-through from the local communications tower. Things like this will heavily dissuade idiots from calling you again.
Sometimes it's worth a small effort.