Google Voice gives you a single phone number and tools to forward incoming calls to any line you want. So no matter where you are--in a taxi, at a satellite office away from your regular desk, staying in a hotel, or anywhere--that single number can ring those destinations at the same time. You just answer wherever you happen to be.
You'll normally control the service from a web browser, but the Google Voice BlackBerry app manages everything from anywhere. In addition to changing your incoming call preferences, you can directly access voicemail recordings and transcripts of those messages. You can send SMS messages from the Google Voice number and place outgoing calls.
Everything is free until you get to the outgoing, international calls. You initiate calls through the software; Google Voice connects your handset and then rings the outgoing number. This aspect is free throughout the U.S., but international rates apply.
Google is still rolling the service out, so you'll have to make a request to join and then wait until there's room for you. But if you already have a Google Voice (or formerly had a Grand Central) account, you can download the BlackBerry app today. Free phone features and instant BlackBerry access make a great combination for any business user.
Zack Stern is building a new business from San Francisco, where he frequently contributes to PC World.