Japan's parliament has outlawed a scam where unsuspecting callers are tricked into calling sex lines, and then charged vast amounts for the call.

Con artists have used computers to call at random up to 3,000 mobile phone users per minute, only to hang up after just one ring.

Curious phone users who ring back to try to identify the caller are played a pornographic message, or they are given information about pornographic services.

They are then billed up to 20,000 yen (�103; $160) for the information they have received.

Jail sentence

Many Japanese people simply pay these bills - too embarrassed to complain or too frightened to object - even though they are under no legal obligation to part with their money.

It took the Japanese authorities almost a year to outlaw the scam, known as the "wan-giri" or "one-ring" ploy.

The parliament's intervention came after "wan-giri" callers twice brought the telephone service in Osaka to a halt in July this year.

From now on, anyone who call masses of people at random and hang up without speaking with them could face a year in prison or a fine of up to 1m yen.