A new US internet telephony provider will offer stiff competition to rivals like Skype and Vonage with a "revolutionary" web-based VoIP that it has launched in the UK.

Jajah is available without registration, contracts, downloads or a headset. Users simply visit the website, enter their own phone number and the destination number (mobile or landline, UK or international) and click 'call'. 

The caller's phone and the recipient's phone then both ring. The caller picks up the handset, and the call is connected.

Unlike leading VoIP provider Skype, Jajah does not remove the cost of phone calls altogether. However, tariffs are significantly lower than with traditional telecoms providers.

A call from London to New York costs 1.2p a minute, and mobile-to-mobile calls are 18p a minute. A complete list of Jajah tariffs is available on the website. 

First-time users get five free minutes to try out the service. Once the five-minute trial is up, the user pays after a call has finished via credit card or bank transfer. 

Jajah co-founder Roman Scharf believes that the service's simplicity is as big a selling point as its cost. "It's so simple my grandma can use it," he said.

Scharf is targeting consumers who don't have the time or know-how to use existing VoIP services.

Firefox users benefit from a Jajah extension that automatically detects and highlights phone numbers on web pages for one-click calling. The service is also integrated in the Plaxo online address book. 

Scharf predicted that Jajah will attract one million paying users by the end of this year. Skype claims 200 million registered users worldwide.