Google Talk is already available for users of Google's Gmail, Google's free email service, and can be downloaded in three minutes. Once downloaded, Google Talk will automatically add their Gmail contacts to their list of people with whom they can communicate using the service.
As well as a messaging service, those with the relevant system requirements will then be able to communicate through voice calls, which Google promises will be as good quality as if the other person were in the same room.
The service is like AIM or MSN Messenger, allowing users to not only type messages in real time, but to talk also. What it is not is a telephone service -- people can only talk to those who have the software and also signed up to the service.
The service is currently available only to PC users, but some of the features will be compatible with other internet messaging services -- although not the free voice call element. Unlike other instant messaging services, such as MSN Messenger, there are no ads on Google Talk.
"At Google, we're continually investing in areas where we can make technological change, and we recognise the importance of efficient instant communications and information exchange," said Georges Harik, director of product management at Google.
"Google Talk further enriches our users' communications experience, whether they choose to communicate via email, IM, or a call."
The move puts the company further into competition with offline companies including the telecoms giants. It has already forced other search engines to up their stakes by the introduction of Gmail last year, offering almost unlimited email storage. Yahoo! and MSN Hotmail both responded by vastly increasing the storage limits on their free email services.
Earlier this week Google unveiled the second version of its desktop search tool, which promises to learn users' preferences and automatically add content that is relevant. It also plans to raise $4bn (£2.2bn) to fund an acquisition spree.
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