We do a similar thing when (annoying) sales people call. You can try to get rid of them as soon as possible. But it is more annoying to them to keep them occupied as long as possible. When I'm disturbed during dinner by ANOTHER newspaper sales call I'll first politely try to say I'm not interested. If they don't take the hit I change tactics and say 'You know, That DOES sound interesting. Let me talk to my wife for a moment' and put the phone down and go back to dinner. 10 minutes later you can just hang up the phone.