That's a good ploy, @thomasn !
It actually costs them next-to-nothing to call you as they use heavily discounted VOIP call rates. They won't like to stay on hold for too long, as one of their performance indicators is linked to the average time spent on each call.
If I have nothing better to do, I try to string them along for as long as possible. Just over 20 minutes is my record. Be prepared for plenty of verbal abuse when they realise their time has been wasted It tends to be really offensive abuse if you can manage to rope in the caller's supervisor as well.