Google (Nasdaq: GOOG) tried and failed to overthrow the business model of mobile phones with the Nexus One Web store. If at first you don't succeed, skydiving really isn't your sport -- and Google is back in the air again. This time, the target is the traditional landline phone.

Now you can call landline and mobile phones for free or cheap, right from the Gmail window on your computer. After a couple of false starts and tantalizing hints, you no longer need an actual phone to make calls through Google's services: The new voice calls in Gmail feature removes yet another obstacle to dropping your landline subscription, as this solution will work well for anyone with a decent Internet connection but spotty or nonexistent cell phone coverage at home. I can also see road warriors using this instead of expensive hotel phones or limited cell phone minutes.

The service is available today, though you need to install a voice-handler plug-in for your browser before enjoying the convenience of free long-distance and cheap international calls from your computer. Google doesn't expect to make a killing on mostly free and ad-less voice calls, but anything that extends the reach of those pinpoint-marketing Google logins is A-OK with Big G.

In typical Google fashion, there is still plenty of room for improvement. For example, you may need to log out of your Gmail account and back in again before the "call phone" icon shows up in your list of chat contacts, and there's a settings screen for changing details like voice mail access from the new interface, but I get an "invalid number" error when trying to change it.

If this were an Apple (Nasdaq: AAPL) product, you'd have to wait another few months while its engineers iron out every conceivable wrinkle in the experience, but Google prefers to launch early and kill the bugs as they show up. If you're holding your Gmail interface wrong, there will be a fix for that problem in no time flat.

This is potentially a very damaging blow to land-locked phone line operators, from national giants like Verizon (NYSE: VZ) and AT&T (NYSE: T) to local phenoms such as Frontier Communications (NYSE: FTR) or Windstream (NYSE: WIN). Landline customers are already switching to cell phones only in increasing numbers, and this service covers one of the last remaining blind spots for that trend.

Did you take a break from this article to sign up for your very own Google Voice account, or do you hate the very idea of putting phone calls in the hands of Google? Mix the venom and perfume in the comments below.

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