As currently implemented, Google Voice in conjunction with Gizmo allows you to place unlimited free calls to the United States and Canada (and ), but requires you to maintain two separate accounts. Launch the Gizmo software on your Mac to log into your Gizmo account, then fire up your browser to log into Google Voice; calls placed in Google Voice can be redirected to ring your Gizmo account before connecting to the person you're calling. If this sounds unwieldy, it's simpler in practice--but the Google acquisition could mean that it will shortly become even easier.

Google Voice remains an invite-only affair, but invitations are plentiful; ask a friend who has an account. Unfortunately, if you don't already have a Gizmo account, you'll have to wait for Google to complete its integration; just as when it acquired Google Voice (then GrandCentral), the company's not allowing new Gizmo signups until the service is ready for rollout under the Google banner.

Google has the opportunity to shake up the mobile phone market in several ways with this play. I've been using Google Voice as my primary phone number since I signed up for GrandCentral back in its bleeding-edge early release and, as a result, I can switch cell phones and service providers at will--which makes staying out of a contract attractive. Month-to-month providers Virgin Mobile and Cricket have been moving into higher-end data services with more impressive phone offerings and even T-Mobile recently moved into this market with a (weird) month-to-month plan that works out as  than its on-contract equivalent. Want to try out an Android phone for a few months? No problem, as long as you're willing to pony up full price for a G1.

Google Voice also has the potential of making cheaper phone plans much more competitive; it's amazing how few mobile minutes you can get by on if you plan your hours-long phone calls for when you're in front of a laptop with Wi-Fi. It's less portable than a cell phone, but not by much. There's long been a strange and expensive dichotomy between home and mobile data service: unlimited and mostly cheap at home, metered and mostly expensive in transit. Google Voice begins to blur the lines between the two and it makes me wonder how much longer the high prices for unlimited mobile data will go without competition from Google or other parties.