Mobile phone users in Japanese cities can now watch digital TV on compatible mobile phones for the first time.
Japanese mobile users can now watch TV on their phones
The service is not the world's first, but it has the potential to be the biggest, by reaching more subscribers than in any other country.
Finding new phones in Japanese shops has proved difficult as only limited quantities have been produced so far.
Japan's 90m mobile phone users can already play video games, send emails and check websites on tiny handsets.
The new service has been carrying test transmissions for several months and will remain free while mobile operators assess its potential and the number of subscribers.
Broadcasters Nippon Television, Fuji Television and TV Asahi are among the companies which have signed partnerships with mobile operators.
'Preparing specific content'
"In the short-term, digital terrestrial broadcasting on mobiles with the same programming as normal televisions will be of little interest for us," said Masao Nakamura, the CEO of Japan's top mobile operator NTT DoCoMo.
"But we are getting ready by preparing new specific content for the service that could come into use later when new channels are available."
Japan's major mobile carriers say sales of compatible phones have been good, but they have not yet disclosed any figures.
Subscribers can watch up to nearly three hours of uninterrupted television with a normal battery.