Internet firm Google, best known for its search engine, has launched free phone calls on the net.
Other firms, such as Skype, already offer such a service but Google claims its version is simpler to operate.
The service has launched in the US, and while Google said no timescale is in place yet for its global roll-out, the announcement has rocked other telecoms operators.
Google Talk is a downloadable Windows application which allows Gmail users to talk or send instant messages. Calling friends is made possible via a computer microphone and speaker. Speech signals are then converted into a digital format so it can be transmitted over the web.
Only Gmail account holders will be able to access the service. To sign up, users must log onto the website and enter their mobile phone number. They then receive an invitation code via a text message which allows them to open an account.
Once they are on Gmail, users can make voice calls, send emails or instant messages (IMs). It is working with other networks to allow voice calls to be made between them, the company said.