Beta for now, but will be open for all soon (U.S. only for now). And it's a free service.
Official Google Blog: Here comes Google Voice https://www.google.com/voice/about
From PC World...
Google Re-Launches GrandCentral Phone Service as Google Voice
Daniel Ionescu, PC World
Mar 12, 2009 6:44 am
google voice is the new name of google's phone service grandcentralGoogle re-launched its phone management service GrandCentral today renaming it Google Voice. The service keeps most of the original core GrandCentral features and adds voicemail transcripts, conference call functionality, and archived searchable SMS text messages.
Acquired by Google in 2007, the new GrandCentral (now Google Voice) offers you a single phone number to ring your home, work or mobile phones, a central voicemail inbox accessible over the Web and call screening capabilities. One of the core advantages of this service is that your Google Voice phone number can act as your master phone number - allowing you to program it on the fly to forward calls to whatever existing phone numbers you have.
Google Voice is still in closed beta stage but the company expects to open the service up to the public within the coming weeks. Google Voice will be free to use and users will also be able to place free U.S. calls through the service. International calls can be made for a small fee (lower than Skype's or your wireless carrier) with credits purchased via Google CheckOut. Also, Google Voice will remain a solely U.S. based service.
The new interface of Google Voice is designed like a central inbox for all your voice communications needs, much like Gmail is for email. You will be able to route all your calls through a single number (obtained upon registration) that can ring your home, work and mobile phone simultaneously. A central voicemail inbox is available as well, which can be accessed via Web or any of your phone numbers.
You can also use your Google Voice number to send and receive SMS messages, which will be forwarded to your mobile phone. Text messages are then archived and you can search through them. Same is applied to your global voicemail inbox, as Google Voice transcribes your voice messages (not very accurate at times) and then they get archived and become searchable.
Google Voice also lets your blacklist and screen your calls. Using Google Contacts, you can create groups and decide who can reach you, on which number and whether they are directed to voicemail straight away or put through to you. Google Voice's voicemail feature also allows you to screen calls by listening in to someone as they leave you a voicemail message and then pick up from there.
Google Voice 
