Which webcam you need will largely depend on the type of calls you want to make. Single caller to single recipient is the most common scenario, but you may need to be able to chat to several people simultaneously, often in separate locations.

There's also the issue of compatibility. While many webcams work with Windows and Mac, some use special drivers to support extra functions. These are often available only for recent versions of Windows.

In general, you shouldn't have any difficulty getting your webcam to work with the most popular instant-messaging (IM) services, Yahoo Messenger and Windows Live Messenger. Not all devices are Skype-certified or will necessarily work with your or app.

Skype is the best-known internet telephony service, but there are lots of others that use a setup known as software internet protocol service (SIPS).

If you're using an older PC or a netbook, hardware specifications may also need to be considered. To record video, you'll need many megabytes of hard-disk space and a capable processor. The hardware at your disposal will also influence your choice of webcam - not all laptops can cope with a high-resolution display and fast framerates.