Free phone calls via the net sound tempting but the technology is not ready for prime time, says a report.
Soon phones and computers could use the same network
Testing of six free net call services by Computing Which? found variations in how easy the systems were to use, call quality and extra features.
Despite being described as free many services made users pay to call anyone outside their community of users.
Which? said people should maintain a landline as the UK emergency services cannot be called via net phone systems.
Testers for Computing Which? put net phone services from Skype, Yahoo, Google, MSN, Babble and Sipgate through their paces.
Such services have been in the news because they let consumers make calls for free or for a fraction of the price demanded by many other phone firms.
Many ex-pats call family and friends back home using net phone services to avoid high international call costs.
In the test Skype topped the list for ease of use and, according to the testers, did the best job of taking users through the process of downloading software and setting up a PC to make calls.
"Some people had trouble figuring out where to plug in the headset in, but once that was sorted it was plain sailing," said Kim Gilmour, senior researcher at Computing Which? who co-ordinated the testing.
Particularly useful, said the Computing Which? testers, was the ability to make a test call via Skype to ensure the system was set up correctly.
NET PHONE SERVICES TESTED
Yahoo, Sipgate and MSN provided an audio helper program or "wizard" to test microphone and sound volumes and quality. Babble was criticised for its poor help files.
The test of the six services also found some variety in the clarity of the calls made across the various networks. Skype was singled out as best for sound quality with Yahoo, Google Talk and Sipgate close behind.
However, the quality of voice calls made across the Babble and MSN networks was more variable. Testers of these services said occasionally calls sounded "tinny".
The different services offered a wide range of features such as voicemail accounts, conference calls and address books but, said Ms Gilmour, users should check the list before signing up.
Some services, such as Google Talk and MSN Messenger do not yet let users call land lines.
All the services tested offer free calls between the users of that particular service. But, said Ms Gilmour, going beyond this immediate community meant paying for calls.
This was significant because the net calling industry was divided into communities defined by the service people use.
Also, she said, there were some other costs associated with using these services.
Users need a broadband net connection, a PC that has a sound card with a microphone input and a headset to make net phone calls.
Despite the success of net phone services Ms Gilmour said they still had their shortcomings. She said: "They are not meant to be a land line replacement because people need that land line for emergencies or if the power goes down."