Two years after acquiring GrandCentral, Google is about to open an updated version of the service to all US users. Google Voice is a free service that provides one number for all your phones, so you can add some features that help you manage phone calls: blocking calls, recording calls, answering from any of your phones, transcribing voicemail and more.

NBC reports that the service will start to be publicly available today and Google confirms the news: "Invites to people on reservations list starting to go out today." In March, Google Voice was released as an upgrade to the existing GrandCentral users and you could request an invitation using a form from Google's site.

Network World found that Google reserved one million phone numbers from Level 3, preparing for the public launch of the service. A major hurdle slowing the adoption of Google Voice is getting a new phone number, but Google tests a feature that allows users to port their existing numbers to the service.