The 3G service, only just emerging in Europe, was launched for the first time in Japan in October 2001 by the country's top mobile phone carrier NTT DoCoMo Inc.

It enables users to transmit data 40 times faster than second-generation (2G) phones, to converse via videophone, and to download short films.

KDDI followed close on the heels of DoCoMo, launching a service the next April, and a third Japanese operator, J-Phone, controlled by the British Vodafone, has announced the launch on December 20 of its own limited 3G service.

Still in their infancy, the 3G networks suffer from partial geographic coverage, weak battery life of handsets and a lack of attractive applications compared to 2G phones, analysts say.

The service has been slow to take off in Japan.

DoCoMo had attracted only 149,000 clients to its 3G service by the end of November, more than a year after its launch. It has sharply dropped its target of 1.38 million subscriptions by the end of March 2003 to 320,000.

KDDI claimed 3.3 millions subscribers in October to its service which analysts consider more of a 2.5G or 2.75G service. It has the advantage of being compatible with its preceding generation, which means it can be used as a 2G phone when outside of the 3G coverage zone, analysts say.

J-Phone has set its sights on attracting a million subscribers here by the end of March 2004, of which it expects 20 percent to be professionals.

It has, for the time being, put the accent less on applications than on international roaming. Subscribers will be able to use their phones in 50 countries at its launch and 63 by the end of January.

"In two to three years most users will use 3G," says Katsuo Hori, telecommunications analyst with BNP Paribas Securities.

He estimates that the 2004 fiscal year, which ends in March 2005, will probably be the first year of real 3G penetration with 30 to 40 percent of mobile phone users in the country using a 3G service by the end of that year.

"After that most users are going to gradually move to 3G," he says.

Hironobu Sawake of JP Morgan Securities Asia estimates that in three years a third of subscribers to NTT DoCoMo, now numbering 42 million, including 35 million who use its mobile Internet system i-mode, will be on a 3G service.

The proportion will be the same for J-Phone but close to 100 percent for the mobile clients of KDDI, according to Sawake.

A company like DoCoMo will be forced to transfer its clients to new networks because of the saturation of its capacity which has harmed the quality of its vocal transmission, says Mark Berman, telecommunications analyst with Credit Suisse First Boston.

The extension of these services is going to accelerate here by the end of 2003 as KDDI passes completely over into 3G next autumn and the NTT DoCoMo and J-Phone coverage enlarges.

On top of that, DoCoMo is due to launch at the end of the month a handset with a battery life of 150 hours on standby compared to 125 for the last model and only 50 for the oldest.