Taking the step further, Google has now come up with official Chrome Google Voice extension. If you are a Google Voice user, you will find it extraordinary.
The extension is pretty nasty on features, it adds click to call functionality to web pages. So if there is a phone number on a web page, like a Online directory, or Email page or your online address book, it will now have a hyperlink. Click it and Google will throw you a pop up window asking which phone you want to use (Home, mobile, work, etc.). It tehn routes the call as per your preference.
In addition, it adds a small button besides the addressbar. You can type in a name or phone number and call or sms it from the browser, and read recent text messages and transcribed.
As far as I tried, I found it working on all three popular platforms: Windows, Mac and Ubuntu.
On the Integration front, lack of an API for Google Voice makes it hard for 3rd party applications to use it via web. To harvest anything useful, it needs to take user credentials, everytime. This Firefox add-on integrates with Google Voice using same concept.
It won’t be long before Google integrates Google Voice with Gizmo5 and Gtalk. Probably, after that having a voice mobile subscription would make no sense. All you need would be a smartbook/smartphone with data-only subscription to do all your voice calls.