About Google Voice on Android
You can use Google Voice for your voicemail service, in place of your mobile carrier’s voicemail service. Google Voice gives you a visual interface to all of your voicemail messages—you can access your messages in the order you want, read transcripts of your messages, and listen to your messages, using a karaoke-style interface that makes it easy to replay any part.
You can also use Google Voice to make international calls, in place of your carrier’s long-distance service, to take advantage of Google Voice’s low international calling rates.
If you already have a Google Voice account with a Google phone number, you can configure your phone to place some or all calls via Google Voice. The people you call will see your Google phone number instead of your cell phone number as your caller ID.
Google Voice is currently available only in the United States.