Everyone must play with GrandCentral.com. This is the coolest bunch of phone tricks.
You sign up for a free account, and pick a new phone number in your area code. Then you configure your other phone numbers, such as cell and office and home. Then people call you at the new number and the appropriate phones ring.
The ultra cool stuff includes recording the calls, and listening to the person leave voicemail. Just like screening with an answering machine, you hear what they are saying to your vmail, and can jump in if you decide to talk to them. You can have different ring sounds based on who is calling.
Play with it. Love it.