Hong Kong is a city that seems to delight in the production of noise; and noise pollution is often overlooked as concern is focused on contamination of air and water. Even so, it hardly takes an academic study, such as the one published at the weekend by the Chinese University of Hong Kong, to reveal that mobile phones - the noise they make and the noise made by people using them - can be very irritating indeed. Users yelling into these ubiquitous instruments can ruin the enjoyment of concerts, drown out dialogue in cinemas, and submerge restaurant conversation. But, apart from identifying an obvious problem, researchers at the Chinese University have no remedy to offer, other than suggesting notices are posted in public places, reminding users to speak quietly and have consideration for others. In truth, that is about all that can be done. It is impossible to legislate for courtesy, and Hong Kong will never win prizes for good manners. Only when it is considered juvenile and unfashionable to be seen constantly shouting into a mobile phone, will matters improve. Irritations aside, the survey does raise the more serious problem of the widespread practice of car drivers using handheld phones. Legislation, which is planned before the end of the year, is appropriate in this case and should be welcomed. The mobile phone has proved itself to be a vital accessory in modern life. But two thoughts should be drummed into users: use it appropriately and keep the noise down.