Google Voice is a free service from Google to use as a centralized phone number with many features including text transcription of voice mail. Google Voice is currently only open for Grand Central members and Google will invite those who signed up after Google purchased Grand Central.

Twitter has given us a hint of when to expect the invites: “GV invites still coming…don’t be discouraged:) Starting with the GrandCentral list and moving on to the GV list. Will take a while.” tweeted  Google Voice manager Craig Walker.

Google has reserved one million phone numbers from Level 3 Communications.  It’s an IP-based phone managing service that routes home, office and mobile calls through one phone number.

A phone connection is required for the service. Google Voice users call into their voice mail service from any phone. Once there, they can push a button to get a dial tone and call a different number. It doesn’t require special equipment to connect to the Internet.

Google Voice features one number, screening, call-blocking, voicemail transcription, SMS support, conference calling, GOOG-411 integration, and call recording, low cost international calling. They also integrated GrandCentral with Google accounts and Google address books. Google reportedly will make their money from the fees for international calling.

The call blocking service, sends the caller “We’re sorry the number that has been disconnected or no longer in service.”

You can still sign up for an invitation via the Google Voice web portal