I have a personal rule of "if it reads 'Restricted,' I do not answer." Basically, if it's someone I'd care to talk to, I already have their number, or it'd appear on my phone.

That said, one time someone called me and just started asking questions. I sarcastically would re-stress the question back to them. (i.e. Who's your girlfriend? >> Who's YOUR girlfriend) Eventually they hung up. No one can prank call me, I can smell phony.

That said I did randomly dial a number and someone answered. We talked for about ten minutes until he said it was time to take his family out to dinner. Seemed like a nice guy.