Last month, Google sent invitations to people who signed up to test the service that is based on technology from GrandCentral, which Google acquired in 2007. Google Voice gives users a single phone number that will ring his or her home, work and mobile-phone numbers. Users can control the service to have specific callers ring a particular phone. Callers can also be sent to voice mail, with messages transcribed and e-mailed to the user.

Writing on The Official Google Blog, Vincent Paquet of Google's voice team and Marcus Foster of Google's mobile team said the application can be downloaded from a Google site and the Android Market. They also said Google is responding to requests to make outgoing calls easier.

"Previously, to place a call using Google Voice, you had to dial your own Google Voice number from your cell phone or use the Quick Call button online," they wrote. "With this new mobile app, you can make calls and send SMS messages with your Google Voice number directly from your mobile phone. The app is fully integrated with each phone's contacts, so you can call via Google Voice straight from your address book."

They also wrote that Google Voice users will be able to access SMS messages sent to the Google Voice number even if a user's cell phone doesn't receive SMS. The app also displays the user's Google Voice number on outgoing calls and SMS messages.

For people who don't have a BlackBerry or Android device, a mobile Web version of the Google Voice site can be accessed through a mobile browser, Paquet and Foster wrote. A Google Voice account is required, and the service is only available in the U.S.