(FORTUNE Small Business) – Yonah Lloyd is itching to hang up on me. I haven't said anything to offend him, but nonetheless Lloyd, vice president of business development at Internet phone company Net2Phone, wants off. He wants to call me back on his Net-based superphone to demonstrate what he's touting as the future of the office telephone. I'm a bit wary. Like most people who have tried Internet telephones using a PC, plugging a microphone and speakers into the computer, I've been less than wowed. If you want to make calls that sound as if you're shouting into a walkie-talkie from the beaches of Normandy while German artillery pounds your position, well, it's perfect. But Lloyd is undeterred. He tries me on the superphone, and I have to admit: The phone call of the future sounds pretty darn good today.

If you haven't yet heard the pitch for voice over IP (as the know-how that makes Lloyd's superphone work is known), rest assured, you soon will. Net2Phone and its rivals are busy lining up distribution partners--cable companies and network providers that will sell voice service along with your Internet access and will become, in effect, your new phone company. This is not the computer toy I've played with before. Indeed, you don't even need a PC: It works with a phone that you plug into your broadband Internet connection to make calls.

Net phones, like cell phones, require little up-front investment. The vendors will sell you (or even give you) a phone and charge a low per-minute rate or fixed monthly fee for a package of minutes. There's no installation charge, and the equipment is fairly inexpensive, typically $150 to $200, and often, like your cable modem, provided free when you sign up.

But should you bite? Are the cost savings and the features compelling enough to justify dumping your old phone lines? Most important, is the call quality good enough for conducting business? Let's put it this way: Don't go ripping out those phone jacks just yet.

I spoke--and even listened--using Net phones from five major players: Net2Phone (the one vendor that sells directly to businesses as well as through partners), Dialpad Communications, Gemini Voice Solutions, Pagoo.com, and Vonage Holdings. In all cases the voice quality was decent, with no one significantly better or worse than another. I had no problem understanding the person on the other end, but it's not quite what you'd get on your regular phone. Voices had a certain metallic inflection, and occasionally there would be a pause that went on a little bit too long. There was also some background noise, like someone rustling papers or talking from the street. Instead of rivaling Ma Bell, they rivaled really good cell phone calls.

The only conversation in which I was hard-pressed to tell I was speaking over a broadband connection was a speakerphone call with a couple of Vonage executives. But when Carlos Bhola, the president of the company, picked up the handset to show me how it sounded one-on-one, he now had that telltale tinny rasp to his voice, as if he had developed a cold in the three seconds it took him to grab the handset. Maybe Bhola noticed it too, for he quickly put me back on speakerphone.

With Net phones still no match for the equipment you already have, vendors are, not surprisingly, talking up nifty new features only a Net phone can deliver. Like Blast Me, in which an incoming call is forwarded to every telephone you own--cell, office, home. You can even assign different area codes to different broadband phones in an office, so a small New York-based business can have 212, 312, 213, and 202 numbers, making customers think you have branches all over the country.

And thanks to the emerging technical standard in Net-based phones, called session initiation protocol (SIP), you'll eventually be able to do things like merge your phone with your sales-force automation software--so that when a call comes in from someone who owes you money, it'll go right to accounts payable. But the emerging standard is just that, so there's no true killer app today, and most Net phone packages come with a ho-hum set of features, like call waiting, caller ID, and voice mail.

Service is another part of the Net phone vendors' pitch, but service cuts both ways. No doubt being able to check billing information in real time or provision new lines from a Web page (instead of waiting for your Baby Bell to send a truck) is convenient. However, when you can't perform self-service, you may be in a mess. Your new phone company will be the cable or network provider that's partnered with the folks who made your Net phone. Perhaps you've been spectacularly lucky, but I have enough trouble getting my cable company to fix my cable modem or unscramble HBO. And even the 10% of more complex customer service queries that will go to the startups may overwhelm them. They are all small companies founded in the past half-dozen years without giant support staffs. Pagoo has 110 employees--total.

Even if you're interested, a Net phone can't replace what you currently have because it doesn't work with emergency services like 911. For now, Net phones are marketed as an additional phone line for making long-distance calls. Net2Phone's hardware, for example, can be set to recognize local calls and send them out over the traditional voice network.

So why the heck would you want this thing? In a word, price. Cost savings are particularly compelling for long-distance calls. A Dialpad call to anywhere in the country, for example, costs 4 cents a minute. The savings are far less significant for local calls for which you're already paying a flat rate or a low per-call rate.

Although the deregulation of the telecom business and the specter of free Internet calls have brought down long-distance rates in the past few years, Net phones' price advantage is still there, making their best trick the oldest one in the book: They can save you money. So when you hear the pitch about the cool tricks and the great sound, tune it out and grab your calculator. If you make a lot of long-distance calls and you don't need the acoustics of Carnegie Hall, this newfangled technology may make sense. Just be warned: The only person likely to be dazzled right now is your accountant.