By Mark Ward BBC News Online technology correspondent

The pair are among the tiny minority that have made phone calls and downloaded data across some of Britain's third-generation mobile phone networks.

The networks currently have no paying customers, but all the firms planning 3G services are furiously testing the technology to ensure it works well when people sign up.

One 3G network goes live in March and others could open for business by the end of the year.

Complexity theory

"The operators do not want the customers to be testing the network for them," said Mr Cook, product manager for Hertfordshire-based Ubinetics.

The company makes hardware and software that helps mobile firms test networks to find out how they will cope with the peaks and troughs of phone use.

Everyone grossly under-estimated the time that it was going to take John Dixon, Ubinetics

Mr Cook said that 3G networks needed new testing tools and techniques because they use fundamentally different methods to let people make calls, swap messages and look at web pages than existing networks.

For instance, in contrast to second generation networks, the geographic area that 3G base stations serve are not fixed.

Instead their catchment area expands and contracts as the pool of users within it make more or less use of their phones.

This expansion and contraction ensures that there is enough bandwidth for people to make phone calls and that data transfer rates stay high.

3G NETWORK OWNERS

Hutchison O2 Orange T-Mobile Vodafone

It also means that phone firms can tune the network to fit demand. They can offer different amounts of bandwidth to different customers depending on what they are paying.

Mr Cook said operators were now grappling with the implications that these load management and balancing issues have for the way they run their networks.

They were also conducting testing to ensure that phones switch smoothly between 3G and existing network technology, he said.

The fact that the old and new technologies had to co-exist made the situation much more complex.

Test pattern

John Dixon, a senior vice-president at Ubinetics, said before now operators had carried out so-called "golden path" testing that finds out if everything works as it should.

Now "negative" testing was under way to explore what happens when handsets or network nodes do not respond as expected during everyday activities such as making phone calls or sending messages.

Hutchison expected to launch Three in March

Mr Dixon said that these testing and compatibility issues meant that early estimates of switch-on dates for 3G networks were wildly optimistic.

"Everyone grossly under-estimated the time that it was going to take," he said.

Currently only Hutchison has confirmed plans to launch its 3G service, called "Three" in 2003.

This is despite the fact that licences for 3G networks were awarded in April 2000 and telephone firms initially claimed services would launch in 2002.

Mr Dixon said that many of the other mobile phone firms had their networks installed and working, even if they had not currently announced when they will be ready for customers.

"I think what would surprise people is the number of [base stations] that have been deployed by network operators now in the UK," he said.

Key areas such as the M4 corridor, London and the UK's larger conurbations are already covered with masts, said Mr Dixon.

He added that the criticism of 3G was reminiscent of the scepticism with which existing mobile phone technology was hailed more than a decade ago.

"I can remember when people said GSM stood for 'God Send Mobiles'," he said, "you could not get them for love or money."

Despite the delays, Mr Dixon and Mr Cook were convinced that the 3G services will be a hit with consumers.

"I think people will be surprised at how far the technology is advanced," said Mr Dixon.