By Oliver Woods BBC World Business Report

A business con known as "one ring and cut" is making life difficult for millions of people in Japan.

They have had their phone service disrupted by a scam, which could earn the firm behind it thousands of dollars.

Phone lines in Osaka and the surrounding region were jammed on Monday - the second time this month - as a result of multiple calls made mechanically by one company.

The company involved has over 200 phone lines and programmes them via a machine to make calls every few seconds to different mobile phone numbers.

Service suspended

The phone hangs up after just one ring leaving a number to call back.

If the people at the other end of the line do call back then they get a recorded message of some kind, sometimes for a sex service, and are charged a premium rate for the call by the subscriber at the other end.

Because of privacy laws we don't even know the name of the company

Justin McCurrey, Daily Yomiuri

Justin McCurrey of the Daily Yomiuri newspaper in Japan said the mystery company placed 4,000 random calls every three minutes to mobile phone users in Osaka and neighbouring region on Monday.

"These people answered the calls and as a result the NTT telephone exchange in this area simply couldn't cope with the volume of calls and had to suspend the service for almost four hours," he said.

Counting the profits

NTT had said it can't release the name of the company making the calls because of privacy legislation.

Mr McCurrey said it is hard to know how much money is being made by the scam.

"In the past the people who were operating similar scams have induced people to make that returned call and have charged them tens of thousands, maybe even hundreds of thousands of yen, just for a telephone call that lasts a matter of seconds or minutes at the most," he said.

Five million lines were tied up by this scam on Monday.

NTT West says it has cut off service to one company which is suspected of initiating the calls.

Campaign

Mr McCurrey said there is no law to stop this kind of activity but NTT itself is heading that campaign for government legislation.

"I don't know whether there is any particular group that represents mobile phone users but if one were to be formed I am sure the pressure eventually would be too great for the government to resist," he said.

The Japanese are the most enthusiastic users of mobile phones in the world and presumably whoever is perpetrating the scam is banking on the fact that most people find it impossible not to return a mystery phone call.