As a pretty strict rule, I don't answer calls from numbers that I don't know.

I have a Windows Mobile 5 phone (Cingular 2125) which I LOVE. It synchronizes my contacts from Outlook perfectly. So, when someone calls that I know, the phone displays the person's name/info, along with the phone number (and it shows if it's home or mobile or fax, etc.)

So, when only a number is displayed on my phone, that means I have no data in my contact list for that number. I let those go to voicemail. Then after listening to the message, if it's someone I know, I put their number in my contact list so that I don't ignore their call next time.

HOWEVER... if they don't leave a message, or if I just don't recognize the number, I'll simply plug the number into Microsoft Live Search or Google, or www.800Notes.com and get LOTS of information about that number. 800Notes is GREAT because people put in who it was that called and WHY they called... it's often telemarketers or people trying to sell you something... this is a VERY cool way of seeing who is calling you...