That situaion is one of the benefits of going by your middle name and having a difficult last name. When I get a call for Thomas, Tom or they have great difficulty with my last name; I then know I'm going to have some fun. I tell them they need the other Mr. Dalrymple and put my son on the phone (worked better when he was younger), I answer questions with unrelated questions. I ask for their home phone so I can call them later, when they say they can't do it because they don't take business calls at home, I say exactly. I ask them to hold on and go away for 20 minutes at a time, for some reason they're never there when I get back to the phone. While I'm talking to them, I call loudly for my "medication" making it clear that it's psychiatric medication, I may really need some soon, you never know. I haven't resorted to singing to them, I don't want to be arrested for manslaughter. One of these days I'm going to act like I'm being murdered, something like describing the knife in graphic detail, then screaming and dropping the phone; well you get the picture. I've yet to make it an obscene phone call, easy to do without breaking any laws.
Dean