Let me let you people in on a little secret. I have caller-id, and for over five years I have refused to answer any calls unless I knew exactly who was calling.
"Private Caller" - not answering. "Out of Area" - still not answering. "Cellular Call" - Nope. "Some person I never heard of" - still not going to answer.
I dont' care if you let the phone ring 500 times, if I don't know who you are I'm not going to answer it. Never.
Sometimes even if I DO know who you are I'm still going to just let it ring. It's my phone.
And there's no answering machine either. So ha ha.
Give up. If I haven't answered by the fifth ring I never will. You're wasting your time.