Michael Arrington was right when he heard GrandCentral was either in talks, or has already been acquired by Google. Today Google announced the acquisition on their official blog, though the terms have not yet been disclosed. If Arrington was correct, it's safe to presume it was around the $50 million dollar mark.
What does this mean? Well, we can only speculate, but it could have a huge impact in several areas for Google. First, imagine having a single, always-on, always-ready, forever available, telephone number that is tied to every phone number you currently have. By signing up, you will have simplified your life and that of anybody else who tries to contact you.
Now imagine having that single phone number tied to your Google Talk instant messenger and Gmail. You can receive phone calls directly on your computer from anyone and listen to voicemail right in Gmail -- the latter of which, interestingly enough, can already be used today.
The service is currently now in private beta -- you will need an invitation to set up a new account now. You will also find that it only works for American phone numbers so far. There is no word on upcoming features or plans to expand to other countries at this time.