I've just discovered something kind of cool: if you want to place and receive free Google Voice calls via your computer, leaving your phone out of the loop altogether, it's now possible to skip the installation of Gizmo, relying instead on the functionality already present in GMail.
I was playing with the settings for Gizmo while trying to improve my method of making free, minute-less VOIP calls from my Android phone and noticed that it now has the option to forward some or all calls to your Gizmo number over to Skype or Google Talk. If you opt for Google Talk -- and if your operating system supports it1 -- you can answer/place calls just using GMail's chat system. It's as easy as when you try to find o2 Mobile Phones, there's nothing complicated about opting for Google Talk. No otherwise-unused software to install at all.
1a) Create a Gizmo account here (if you don't already have one)
1b) Configure Google Voice for use with Gizmo following these instructions (if you haven't already done so)
3) Scroll down to the 'Forwarding' section. It looks like this:
4) Select 'forward all calls' and put in your GMail username in the appropriate field and Click 'Save.'
That's all the configuration that's required.
Now when someone calls your Google Voice number, in addition to your phone ringing, your GMail (or Google Talk desktop client) will beep at you telling you a call is incoming.
If you want to place a call, you just need to use Google Voice's web interface. Click 'Call,' put in the desired number, and then select your Gizmo number as the callback number. Your GMail will then ring. When you answer it, you'll hear the number you just dialed ringing.
1: Unless you're a freak like me running some crazy non-Windows, non-Mac operating system you'll be fine. If you are a freak like me, you can either keep using Gizmo, or have Gizmo auto-forward your calls to Skype and do it that way.
Today, after some tinkering, I accomplished something of which I've long dreamt: placing a Voice-Over-IP call, from a real phone number to a real phone number, from my Android phone, using only my 3G/EDGE data connection. No plan minutes or hosted PBX phone service involved.
Here's a brief how-to (that's not even dependent upon having an Android phone):
1) Get Google Voice. (This step is going to be kind of a buzzkill for most people, as Google is still in some sort of indeterminate closed beta with the Google Voice system. I'm not exactly sure how I ended up with access, so I don't know what to tell you to do to get it too.)
3) In your Google Voice settings, add the 'SIP' address that Gizmo gives you to your Google Voice account, selecting 'Gizmo' as the type of number. (Detailed instructions.)
4) Install a Gizmo-compatible client on your phone. The folks at Gizmo have written clients for many popular phones. You can get one at http://gizmo5.com/pc/products/mobile/. If your phone supports 'J2ME,' then chances are they've got you covered.
(On Android, I installed 'sipdroid,' which isn't a Gizmo-specific application, but one that can handle any Voice-Over-IP service. (You can find sipdroid in the Android Market, but that version only works via wi-fi. Get the full version which supports 3G/EDGE calling via their site.) Configure it using the info from the Gizmo support page.)
5) Use Google Voice's web interface to tell it to call whatever number you want, selecting your Gizmo number as the one to ring when connecting. (Gizmo offers incoming calls for free; telling Google Voice to initiate a call and ring your Gizmo is technically an incoming call, even when you're calling a friend.)
6) Tell the Gizmo client on your phone to answer the call. You're now connected, and you're not using any minutes.
A nice side-effect of this Gizmo compatibility is that you can run Gizmo clients on any computers you have around. When someone calls your Google Voice number, all the computers will 'ring' as well as your cellphone, so you can answer it from one of them instead. More minutes saved.