One week after its launch, the world's first third-generation mobile phone service has seen some glitches, but NTT DoCoMo is confident that its lead in wireless technology is secure.

An official at DoCoMo, Japan's biggest wireless operator, said on Wednesday that there were no major mishaps and that any glitches had little to do with the core 3G technology, which makes video and music downloads possible because of its fast transmission speed.

Users reported that the battery life for 3G phones was more limited than they had expected, although Japanese subscribers are accustomed to highly advanced cell phones that can remain on standby for as long as 20 days.

Some said that the 3G phone's battery ran out within a day, while others reported that it would go out of range even within the designated trial service area of Tokyo's 23 wards.

A select group of 3,300 users received free 3G phones a week ago as part of DoCoMo's introductory service.

The "soft launch" will give it a chance to iron out any bugs before a full commercial launch scheduled for October 1st.

"On the whole, I am impressed with the speed and the voice quality when it works. I'm impressed with the speed of the i-mode (Net access) service," said an employee of a technology firm who has a standard 3G model phone made by NEC Corp.

"But it did freeze on me once and cut off a few of my calls."

DoCoMo said recently that its 3G service would be nationwide in a year.