Cellular phones have become so popular--and their users so un- popular for disturbing everyone from theatergoers to train passengers--that the arbiters of manners have been forced to step in. A German manual, Style & Etiquette, already has a section devoted to proper use of a mobile phone. The book advises, for example, against taking a cell phone to a job interview: it might ring at the wrong time and convince your prospective boss that you are self-important and insecure. And please, the author beseeches, have respect for the dead: turn the thing off at funerals.

Such common-sense suggestions are only the beginning, of course. Here's our correspondents' guide to going cellular without making an ass of yourself:

Do not say anything on a mobile phone that you wouldn't like to see on the front page of a tabloid. An eavesdropper picked up Britain's Prince Charles making verbal love to his paramour, while Princess Diana was caught in an intercepted cell-phone chat that revealed not only an amorous liaison but also an embarrassing nickname: "Squidgy."

Do not use a mobile phone in places where people have paid big money to listen to voices other than yours. La Scala opera house in Milan has had so many complaints that Rule No. 9 for ticketholders is, "Leave telefonini in the cloakroom."

Do not take a phone into a stuffy British men's club. The Athenaeum warns its members that all mobile phones must be left with the porter. White's members, the club secretary hints, are far too well mannered even to think of carrying one inside the club, and Gavin Rankin, who helps run London's posh dining club Harry's Bar, says, "Any attempt to use one would be swiftly suppressed."

Do not use one on Paris buses. Last month riders of one bus watched as a physical therapist who took an important call from a patient was loudly berated by an elderly woman passenger who cried, "Elitism! They can't afford Rolls-Royces, so they ride the bus with portable phones to impress people."

Do use a mobile if you want the latest in gangster chic. Last March during the kidnapping of German tobacco heir Jan Philipp Reemtsma in Hamburg, the bad guys used a cell phone to direct the ransom couriers to the drop-off point. And in London etiquette maven Mary Killen complained of the mobile phone's "very visible popularity among petty criminals."

Do be careful who borrows yours. Warns Milan management consultant Antonino Busacca: "The problem comes when a husband lends it to his wife and then his lover tries to reach him."

Do remember that how you use your phone reveals a great deal about your character. "When you go out for a pizza with friends," says Angele Becheras, secretary for a French news agency in Rome, "you see there are two kinds of people. Those who turn their telefonini off. And those who leave them on, put them on the table and hope someone will call." --By Jay Branegan. Reported by Greg Burke/Rome and Rhea Schoenthal/Bonn