Difficulties in interoperability between handsets, operator networks and software platforms now represent the biggest obstacle to the development of third-generation (3G) mobile data services, and could delay the launch of robust commercial services in the UK by another 12 to 18 months.

Vendors such as Nokia and Ericsson are implementing complex testing procedures alongside mobile operators and software developers to ensure their phones, networks and applications can communicate, but the process is likely to take a long time.

"The critical phase is interoperability testing," said Juha Seppa, director of solutions and applications for Nokia Networks. "Now that the handsets and infrastructure are maturing, we must look at various implementations to ensure handsets are interoperable, then look into the interoperability of both applications and services."

And while standards bodies such as the 3rd-Generation Partnership Project are defining the 3G technical specifications that have to be met, the push has to come from vendors themselves, according to Gartner analyst Jason Chapman.

"Various players accept they have to compete, but it is in everyone's interests that interoperability issues are resolved rather than worrying about divulging information to rivals," he said.

Manx Telecom, a wholly owned subsidiary of mobile operator O2, has been testing 3G services on the Isle of Man since December last year, using handsets manufactured by NEC and Motorola.

But 10 months on, no commercial service is yet available, indicating that significant problems still remain.

Hutchison 3G, which was set to begin a first-phase 3G service to between 500 and 1,000 customers in the UK and Italy last week, will also be carrying out testing.

Nokia's forthcoming 6650 3G handset will offer maximum bandwidths of 64kbps or 128kbps, ostensibly to avoid overloading unproven 3G infrastructure.

"From the start 384kbps will be viable, but practical data speeds will be lower," Seppa said. "Over the next 12 to 24 months, they will increase to 512kbps and beyond."