For the past few weeks, I've been working on a big story about voice over the Internet--a.k.a. VoIP or Internet telephony. In the process of doing this piece (which should appear online early next month), I've been using the technology a lot. I think it's fantastic: with the right setup, you will get better quality calls and much better features, and as a bonus, you'll spend less money. What's not to love?

Well, I've also uncovered some snags that are bugging the heck out of me. They are the VoIP "gotchas." Here's what they are and what can be done about them.

Variable quality. I've been using Skype, a PC-to-PC voice program, to talk with Matthew Elliott, our networking expert in New York. When we're both on good headsets, we get nearly CD-quality sound and hardly any lag, putting our standard phones to shame. But we've also experimented with a similar system, Free World Dialup (FWD), which gave us tinny sound and nearly a half-second of lag. The problem is, with Internet telephones, you're subject to extremes. When VoIP is good, it's very good--but when it's bad, it's horrid.

Skype uses a proprietary point-to-point architecture, and since Matthew and I were on the CNET private network, we got incredible quality. I don't know what technology FWD uses, but clearly, it's not as good, and it's subject to the vagaries of the open Internet, which affects transmission quality.

If you use VoIP at your home or office, the output will depend on factors you can't control, such as the latency between devices that route your calls. There should be a way for voice calls to demand higher-priority service. If ISPs were to offer this, they could, theoretically, charge extra for it. This is a business opportunity.

Come to think of it, which companies really know how to build dependable, consistent networks, then reliably bill by the nanosecond? That's right: the traditional phone companies. Maybe good VoIP service will end up where telephony has been for a hundred years after all.

Lack of interconnection. The best thing about the traditional phone system is what people take for granted: Any phone on the planet can connect to any other. Some Internet telephone systems, such as Vonage, can also connect to any other phone. But except in extremely rare cases, two people on different VoIP systems can't connect to each other directly over the Internet--they have to use the public phone system as a go-between.

This is partly because different systems use varying standards (Skype and Vonage are simply incompatible) and partly because even systems that use the same technology don't have the peering relationships that connect them to each other, the way the world's telephone and postal systems do. The only VoIP peering I know of is between FWD and Packet8.

This is dumb. Using the phone system as an intermediary costs money (thereby eliminating one of the big benefits of VoIP: free calling) and limits the convenience of each VoIP system. But hopefully this is a temporary problem; companies such as ITXC specialize in phone system interconnects and are building VoIP-to-VoIP clearinghouses.

Can't get there from DSL. DSL, when it's offered, is usually a phone company-provided service and comes with a phone number. If you want to use that phone number with a new VoIP system, though, you have a problem: You can't transfer the number without terminating your DSL service.

What you need is DSL by itself, with no extras along for the ride. This service--sometimes called Naked DSL--is offered by only one phone company, Qwest. If you're a DSL customer on another phone system, the only way you can get VoIP, as mentioned above, is to get a new phone number. So much for number portability.

The telcos should decouple the phone service from their data service. VoIP proves that voice is just an application that runs over a bunch of wires; who cares if they were originally telco wires?

Firewalls. Finally, VoIP isn't as plug-and-play as it could be. While PC-based systems such as Skype have an amazing capability to punch through network firewalls and connect any two PCs for voice calls, other systems that use standards-based calling protocols (such as SIP, or session initiation protocol) can be blocked by older or aggressively set firewalls.

In my house, I couldn't get Vonage to work with my SonicWall hardware. Using a more recently built D-Link firewall solved the problem. But on campuses and in offices, people usually can't swap out LAN components as easily, so there's the possibility they'll be unable to use VoIP off the shelf.

There are companies making devices called session border controllers (SBC) that allow VoIP calls to work through firewalls and network routers. Eventually SBC technology will be built into firewalls, I predict. It'd be nice if firewall and router manufacturers offered upgrades for no or low cost now and, thus, stay ahead of the emerging SBC market.

As I said, I like VoIP generally. But I'd appreciate it a whole lot more if vendors could figure out fixes for the "gotchas."