Google Voice has been out for about a year now and up until today, you had to request an invitation to use this service. Today, Google has announced that Google Voice is open to the public.
It’s still only available to residents of the United States but offers you free call, SMS messages, voice mail transcripts, and having one number for all your phones. To get your Google Voice number simply log into voice.google.com with your Google account and follow the set-up wizard.
There is a slight charge for International Calls (here's the rate schedule) and while there's still not a Windows Phone mobile app for Google Voice (hopefully that will change), you can still access things through your mobile browser at google.com/voice/m .
[Read: Google Voice Blog]