Google Voice has a ton of great features, and in a lot of ways fundamentally changes the way you’ll use your phone. A lot of things suddenly become easier with Google Voice – checking your voicemail, sending text messages, and more – and they’re all best dealt with through your computer.

But, as of now, Google Voice doesn’t inherently let you make calls from your computer. I mean, I’ve got a microphone and speakers on my computer, as well as a fast Internet connection – why shouldn’t I be able to make calls, ideally for free?

Here’s how to set it up (I did this on a Mac, so PC directions might be slightly different – the same rules will apply, though).

Disclaimer: This is all assuming you’ve already got a Google Voice account. They’re sending out invites at lightning-speed, so if you don’t have one, go get on the list!

1. Download and Install Gizmo5 (create a free account, with no call credits – you won’t need them!).
2. Open Gizmo. In the “Home” tab of the application, click “Edit My Profile.”
3. In the tab that pops up, you’ll see, filled in, a number for “SIP number.” Copy that number (everything before the @ sign).
4. In Google Voice, click “Settings”, and then “Phones.”
5. Click “Add Another phone” and paste the SIP number from Gizmo (again, only what’s before the @ Sign) into the box.
6. Name the number “Gizmo” or whatever you want, and then Save it.

Now, to make calls:

1. Open Google Voice, and click “Call”
2. Enter the number you want to call
3. Make sure the Gizmo phone (whatever you called it) is selected as the “Phone to Ring”
4. Click “Connect”
5. You’ll get a pop-up from Gizmo, with your Google Voice number on the caller ID. Answer it!
6. Google Voice will automatically dial and connect the other person, and you’ll be chatting from your computer!

The whole process only takes about five minutes, and doesn’t cost a nickel. Because you’re using a SIP number, all the data is transmitted over your cable connection rather than your phone network. That means you’ll need fast Internet to really make this work, but also means it doesn’t cost a thing!

Read more: http://www.ghacks.net/2009/07/24/make-free-calls-from-your-computer-with-google-voice/