Google Voice started as an independent service called GrandCentral that was bought by Google Inc. in 2007 and re-introduced as Google Voice in 2009. If you already use Google's Gmail, you should feel right at home here -- the interface of Google Voice is very similar to Gmail's.
Google Voice assigns you a new phone number to link your other phones to. You can also send and receive an unlimited number of SMS text messages through your Google Voice number for free.
You can record multiple greetings and assign each to play for specific phone numbers that call you -- or for groups of phone numbers that you put together via the Google Voice site. So you can, for example, record a casual personal message for family and friends and a professionally worded one for co-workers. You can also instruct the system to send calls from specific people (or groups of people) directly into voice mail.
Once you have a voice mail, you can arrange to have alerts sent via e-mail or SMS, along with a transcription of the message.
Google provides apps for Android and BlackBerry phones that you can use to access your Google Voice account. Owners of other smartphones (including the iPhone) can use the service only through a version of the site formatted for mobile device screens.
On the Droid Eris, the mobile Web page version of Google Voice was simple and rather text-heavy. You can send and receive SMS texts, and listen to your voice mails. You can even make voice calls through it, but this works the same way that it does through the regular Web site -- you click on or enter a phone number, Google Voice calls your cell phone, you answer, then the service calls the number you clicked or entered, and connects you to it.
On the other hand, the free Android app for Google Voice integrated seamlessly with the Droid Eris, so I could use the phone's own dialer to make voice calls through my Google Voice account.
The sound quality of calls made through the mobile-formatted site or the Android app was very good and virtually indistinguishable from a normal cell phone call.
There is an added attraction: You can make calls through Google Voice by clicking on the number you want to call from your Google contact list (or you can enter the number manually). Google Voice first calls whichever phone that you have linked to your user account; after you pick up, the service then dials the number you want to reach. U.S. domestic calls are free, while international calls start at 2 cents per minute to most countries, which is roughly comparable to what it would cost using Skype. In fact, Google's purchase of Gizmo5 , a VoIP service that rivals Skype, in November 2009 probably means Google will soon add Gizmo5's VoIP technology to Google Voice.
The sound quality of calls using Google Voice was better than what I've gotten from some cell phone companies. (The quality of each call depends on many factors, of course, including the provider's network technology, their coverage area and the model and type of phone you use.)
Google Voice (nee GrandCentral) pioneered the Web voice mail market and is still a solid and reliable service. Its current version doesn't let you make calls directly through your computer -- but this limitation is sure to change if Google incorporates its recently acquired VoIP technology into Google Voice.