I am a fan and a regular user of GrandCentral, long before Google acquired Grandcentral. It allows you to use a single number to ring your home, work, and mobile phones, a central voicemail inbox that you could access on the web, and the ability to screen calls.All are very valuable to me.
Now Google has added Voice Transcripts of the voicemail and archive and search SMS texts that you send and receive, when it renamed GrandCentral to Google Voice.
If you're a GrandCentral user, Google says that over the next couple of days, you will receive instructions in your GrandCentral inbox on how to start using Google Voice. If you are not a Grandcentral user and if you'd like to be notified, when the service opens to others, You can send Google your email address.
I am waiting!
Official Google Blog: Here comes Google Voice