Voice over broadband, Internet telephony, Voice over IP (VoIP) – call it what you will, the past couple of years have seen the unstoppable rise of the technology that lets you make telephone calls over the Internet.

There's now a bewildering array of affordable consumer VoIP products and services to choose from. All promise the same thing – cheap or, in many cases, free phone calls, using the spare capacity available on your Internet broadband connection.

Exactly how that’s achieved, though, can vary enormously, as can the features and optional extras included by the providers, and making sense of it all can be a mind-boggling task.

Hence this feature, in which we aim to explain what VoIP is all about and examine the pros and cons of the different home-user products and services on offer.

Newbies start here

Like any new technology, getting to grips with VoIP can be a little daunting. However, the principles behind it are easy enough for most PC users to grasp, and best explained by comparing what VoIP does with an ordinary analogue phone call.

Make such a call via the public switched telephone network (PSTN), and you’re directly connected to the other person by a private analogue circuit.

It's a bit like having a dedicated wire between you and the other phone, even though there may be one or more switchboards in between.

What you say is then communicated as an analogue signal between the handsets at each end – just as it is when you join up a couple of tin cans using a piece of string.

With VoIP, however, there’s no private circuit and the analogue voice signals are digitised and encoded into TCP/IP data packets.

Then, just as with any other network traffic, these packets can be routed across the Internet before being decoded back into analogue voice signals at the other end.

The main benefit to this is cost – or, rather, the lack of it – especially with the ready availability of cheap broadband services.

These provide the necessary bandwidth plus, once you’ve paid for the connection, it doesn’t cost any more to use it, whether sending an email or talking to someone on the phone – assuming you stay within any download limits set by the provider.

Of course, there are a few caveats, not least being the need for suitable hardware and/or software to do all that digitising and routing of VoIP packets.

Plus, for totally free calls, the person at the other end needs to be similarly equipped and, in some cases, a subscriber to the same VoIP service provider.

It needn’t cost the earth to get started, as a lot of the software is available for free and plenty of bundled services come with everything you need for a fixed monthly fee.

Prices are dropping all the time, while service providers are increasingly adding extra functionality – including free telephone numbers to enable ordinary public telephone subscribers to call your VoIP phone and for you to dial ordinary telephone numbers at much reduced rates.

Voicemail services are increasingly common, along with call forwarding, music on hold, SMS facilities and a lot more.

Getting started

So, where do you start with VoIP? Well, one of the easiest and cheapest ways is via a PC-to-PC service such as Skype (recently acquired by Ebay) or those available to users of MSN, Google Mail and Yahoo Messenger.

You typically require a PC to use one of these services, although that could be a handheld device and there are other ways of minimising the PC dependence, which we’ll discuss shortly.

You’ll also need suitable audio hardware; at the very least, a microphone and speakers, or preferably a headset of some kind (which could be wireless for more freedom) or perhaps a USB telephone handset.

The software needed is easy to obtain and doesn’t have to cost anything. If you’re already using MSN Messenger or Yahoo, for example, you probably have everything necessary, while for Skype a free download is available with versions for Pocket PCs, Apple Macs and Linux as well as Windows desktops.

Once this software is up and running, calls to other VoIP users can be made totally free of charge if they’re using the same service.

Connecting to other VoIP services or making calls to people who don’t have VoIP is a little harder and can cost money.

This is primarily because, in order to connect you to the public telephone system, the service provider needs a gateway to make calls to the people you dial on your behalf.

With Skype, two separate gateway services are available: one to let you make outgoing calls (SkypeOut) and another to receive incoming calls on a standard PSTN phone number (SkypeIn).

SkypeOut is a pay-as-you-go service where you buy credit in advance to cover the cost of the calls. SkypeIn is a subscription service costing €30 (£20.72 approx) a year, for which you’ll be allocated a standard UK telephone number and a free Skype voicemail subscription.

Yahoo offers similar gateway services (note that those provided in conjunction with BT in the UK are somewhat limited), while MSN is expected to add dial-out and dial-in facilities later this year.