MUMBAI: After South Korea, Japan has become the second Asian power to launch free-to-air digital TV for mobile phones through terrestrial digital broadcast system.

Digital TV broadcasts for mobile phones equipped with special receivers began in Japan's major urban areas on Saturday, following several months of test broadcasts.

But the new service in Japan, which is free, will potentially reach the broadest market yet through the country's terrestrial digital broadcast system, which relays images through the air via TV towers, not satellites.

It also uses broadcasting air waves, rather than an Internet connection, to relay streaming video.

Although South Korea has offered the service since the end of last year, Japan is a frontrunner in the new technology, popularly known as 'One Seg,' after 'One Segment.'

One Seg takes its name from the one frequency segment out of 13 allocated to terrestrial digital broadcasting that is reserved for mobile phones.

Users with a TV tuner-equipped cell phones, car navigation systems and portable game players will be able to watch the broadcasts free of charge.

If one considers how embedded mobiles are in Japanese life, the service has the potential to be the biggest of its kind in the world, by reaching more subscribers than in any other country.

Handsets have been on the market in Japan for several weeks that are equipped with the service, which can also broadcast programmes onto laptop computers, high-end video-game machines and other terminals.

Mobile operators have lined up agreements with television networks to develop the service. NTT DoCoMo has tied up with Nippon Television and Fuji Television. DoCoMo's main rival, KDDI, has forged a partnership with TV Asahi.

Kazunori Higuchi, a spokesman for NTT, describing how the service works, was quoted in Japan Times as saying: "A viewer is watching a drama and decides she likes the dress the lead actress is wearing. At the bottom of the screen is a link to an online shopping mall. She clicks on the link and buys the dress. Or maybe she just likes the show's catchy theme song and downloads a ring tone of the opening bars."

One major drawback that may hold back the penetration of the service in Japan though, is that handsets with tuners are still scarce and expensive.

Japan has 90 million mobile phone users who already play video games, download music files, exchange e-mail, read news, trade stocks, store digital photos and surf the Web.