User registrations on the Jajah internet telephony service have increased by more than 50 per cent following the major Skype outage last week.

"As soon as Skype went down, we started to see our numbers climb," said Jajah co-founder Roman Scharf.

"Thousands of users searched for alternative ways to contact friends and family and Jajah was ready to serve up endless free and low cost calls."

Scharf suggested that Jajah was a popular replacement because it does not require a download or a contract, and calls can be made using traditional landline or mobile handsets.

Jajah works by allowing users to enter two phone numbers on the company website. The service then rings both parties and connects the call using its internet routers.

Calls between two registered users are free for 30 minutes a day, with charges beginning after that time.

However, Scharf said that there were no hard feelings and, as a "long-time fan", he was happy to see Skype up and running again.

"At the same time, we are glad that we were able to provide back-up for consumers that needed a quick alternative during the outage," he added.

Skype blamed its crash on the latest release of Microsoft's monthly security patches, which caused machines to reboot and overload the service.