What VOIP Can't Do
Along with its many advantages, VOIP also has some limitations. For example, most VOIP companies don't have 911 services. With the money you save, you may decide it's worth keeping a stripped—down conventional phone line for that purpose. For those who get Internet from a satellite provider, VOIP isn't an option, since a satellite receives data faster than it can send it. When used in large numbers, VOIP phone lines can begin to weaken your Internet signal, which may degrade sound quality and slow down your web surfing, but it's unlikely to be a problem with a basic household setup. "In terms of residential applications, one line seems for the most part stable," says Stu Shulman, managing partner at S&S Interconnect, a telephone network installer in New York City. "The voice quality is pretty good."

Shulman points out another significant difference between VOIP and land lines: With conventional phone service, you don't necessarily lose contact when the power goes out. Not so with VOIP. "If you don't have a battery backup on your cable modem and you lose power, you'll lose your phone," he says.

Those drawbacks aside, the VOIP trend is gaining rapid momentum—and everyone may benefit. "Phone companies are going to have to become more competitive with pricing," says Shulman. "You can spend twice as much money with the phone companies as you will with VOIP."

Some websites, like Skype.com, allow you to download software that lets you make free Internet calls, anywhere in the world, to anyone who is using the same program.

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