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V0IP (Voice over Internet Protocol) is the slightly awkward name of a downright disruptive technology that's turning the world of telecommunications on its head. It's all thanks to convergence, the process by which all the different kinds of stuff being carried around the world through different wires are fast becoming the same.

Once upon a time, phone calls, carried as an analogue audio signal over wires installed for the purpose, were a completely different thing from data communications. Telephone technology had the upper hand: when computers wanted to talk to each other, they had to convert their digital signals to analogue using a modulator/demodulator, or modem, so that they could be squirted down a phone line and converted back at the other end. This is how dial-up Internet access still works today, if you're unfortunate enough to be stuck with it.

Recently, though, equipment has been devised that can use those same phone lines to transmit digital data at enormous speeds. This is the world of ADSL broadband, which has made Internet access ten to 200 times faster in just a few years. Cable TV companies - in the UK, predominantly Virgin Media (formerly NTL/Telewest) - can reach even higher speeds over their own new wires. And most of us pay a flat monthly fee for our Internet connection, with no limit, or at least a fairly high one, on the amount of data we can send and receive.

Say goodbye to phone lines

That makes phone calls - which require only a fraction of the bandwidth, yet are often charged by the minute - look pretty poor. And if you've got cable, you may wonder why you need a separate phone line,

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costing you a monthly fee. Well, perhaps you don't. If you could make phone calls using digital instead of analogue signals, and route them over your Internet connection (a sneaky reversal of the process that brought us Internet access in the first place), then calls would effectively be free, along with all the rest of your up- and downloads.

When you think you're sending email or surfing the web, you're really shifting packets of data back and forth using IP (Internet Protocol) networking. Your service provider doesn't much care whether the data packets contain email, photos, video, TV or voice data. So there's nothing to stop you making phone calls over your broadband connection as long as you have the right equipment.

In this article we'll look at some of the products available right now to take advantage of VoIP in various ways, and the services that have been established to help users talk to each other.

It's fair to say that if you're going to use VoIP to the maximum, it may not end up being completely free. The good news is that it'll still be a lot cheaper than using a conventional phone line, and it brings some new features and possibilities too.

Voice becomes data

Any fast Internet connection can be used for VoIP, a clever technology that converts an audio signal into packets of data. The clever part is keeping the transmission going in real time: you don't really notice if some of the graphics on a website load faster than others, but you'd know if your friends' syllables arrived in the wrong order.

Starting with the H.323 protocol and moving on to SIP (Session Initiation Protocol) in 2000, it's been relatively easy for companies to use their existing networks to distribute both data and voice. A SIP telephone system has to connect to a SIP server, so there'll be a price to pay, but companies preparedto invest in such systems can slash their telephone costs. A variety of providers, ranging from established communications companies like THUS (www.thus.net) to recently launched specialists like BlueBite (www.bluebite.co.uk), will happily supply you with VoIP services.