How to Google Voice Work? [Solved]

Google Voice (formerly Grand Central) is currently a call management and routing service.

It's purpose is to give you a single unchanging number that can ring to all of your phones. Your home and cell numbers can change over time, but your voice number won't.  You need to hand out the number to people who will call you for it to be useful.

Calls made from an android phone using your Google voice number actually use your phone service provider to make a call into google's servers which connect you to the number you dialed while displaying your google voice number on the recipient's caller ID (optional).

You can also set your phone to ask you which number you want to call from, each time you place a call.

When you get called on your Google voice number, Google's servers take the call while checking your voice settings to determine where to route the call.

In addition to ringing your phones, it can also ring to your email. I make and receive calls in my google mail all day.

It hasn't yet evolved into a full voip service.  It currently allows you to make VOIP calls from ya computer via Google mail to other Google mail users or even landlines much like skype.

With Google's aquisition of Motorola Mobile last year, a full phone service could be on the horizon, but I don't think it's going to be a free service.  It will likely be competitively priced with other phone service providers. :)

Technical Details:

Google Voice leverages a softswitch which connects to the PSTN via Bandwidth[dot]com's SIP network. It is theorized that Google is running an open-source softswitch, but it is not known which of the many projects they've chosen to use (FreeSwitch, Asterisk, Yate, SipXecs, to name a few).

Google Voice does not currently support SIP registration of handsets or other devices but does provide basic call handling features like "find-me, follow-me", Simul-ring and the prized Voicemail Transcription. Google lacks a number of the business phone features so many organizations cherish and thus hasn't become a commercial offering yet.

Another Way to Google Voice work?

While much like Skype, computer to computer calls using Google Talk or the voice/video plugin for Gmail, are expected to remain free, calls to physical phones could be charged some day like international calls are currently billed, albeit at a very competitive prices.

On an Android phone with Google Voice installed, it is possible to configure your phone in such a way that international calls automatically get routed using Google Voice - avoiding the carrier's prices.