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.