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The beauty of VoIP phone services like Skype is that you can call subscribers anywhere in the world for absolutely nothing. All you need is the right software and a broadband connection. In fact, chat apps from AOL Instant Messenger to Yahoo Messenger are now rapidly morphing into Internet phones, offering a tempting alternative to traditional cellular and landlines. Just download the chat software, plug a phone into your PC, and start dialing. But not all services are created equal.

High on Skype

I'll make it easy. To shrink your phone bills to the size of a pea, install Skype 3.0. It's a snap to use and it's dirt cheap. PC-to-PC calls are free; to receive calls from landlines or cells, you can buy a Skype-In number for $38 a year. To call any phone, sign up for the Unlimited Calling plan for $30 a year or buy SkypeOut minutes for less than 2 cents a minute (international rates can be higher). Ten bucks buys you over 8 hours of gabbing.

Other chat services are scrambling to catch up. For $15 a month AOL's Phoneline allows you to make unlimited long-distance calls, if you can get it to work (I couldn't). Microsoft's Windows Live Messenger (in beta at press time) lets you call out, but cell and landline phones can't call you. Only Yahoo's Messenger with Voice approaches Skype's features, and at $30 a year for a Yahoo Phone In number, it's a bit cheaper. But you won't get Skype's broad selection of area codes and prefixes when you choose your number, and Yahoo's service isn't as easy to use.

The big caveats? Neither Skype's nor Yahoo's service offers 911 emergency assistance. And while PC-to-PC connections can be crystal clear, calls to cell phones or landlines range from adequate to awful. So while Skype or Yahoo can't entirely replace a phone line, either one can supplement it quite nicely.