I've been using GrandCentral for about a year and a half now. The level of control is just stunning.
One number that rings your cell phone, home phone and work phone at once; pick up the call from any of them. Transfer phones during the call.
Different greetings for friends, family, work, and other contacts.
Listen to the message as it's being left. Pick up the call during the message if you like.
Voice mails are available to download as mp3 files. Need to save an important message? You can easily. I've saved messages about projects with other files in my project directory. No more looking for that message. Nice!
Call anyone in your address book from your address book. This is free now, but will be a paid service. I knew going in this wouldn't be free forever - free outgoing calls to anywhere in the country?? I hope they don't overcharge for this - if it's reasonable, it's totally worth a fee.
This service is great and quite solid. If you're waiting for it, hold on... It's worth the wait!