The Seven-Year Itch was defined by one unforgettable sequence when Marilyn Monroe stepped over a subway ventilation shaft and her skirt billowed in the wind, exposing her derriere.

Another classic moment came in The Graduate, when Ann Bancroft leaned forward and offered the youthful Dustin Hoffman tea and a glimpse of cleavage.

In the past year, thousands of women have been "immortalised" at the gym, or the mall, or visiting public loos; while Monroe and Bancroft were posing, these women weren't.

There are a clutch of popular "up-skirt" websites featuring covert snaps of unsuspecting women caught during embarrassing moments.

This is one of the undesirable aspects of the 3G and MMS revolution. The new generation of mobiles allow idiot-proof digital pictures to be snapped covertly and instantly transmitted. 3G devices offer high-quality colour, MP3 format sound, expanded memories and rapid video downloads.

3G also enables live broadcast of films as they are shot. What you have is a recipe for technologically-enhanced harassment.

These features also have invaluable legitimate utility, of course. For instance, architects and urban planners can conveniently refer to design specs.

Normal media stories as well as Tehelka-style "sting operations" are enhanced by the ability to grab pictures easily. And without digicams, the abuse at the Abu Ghraib prison in Iraq might never have come to light.

But 3G and MMS enables a vast range of adult content. This includes visual phone-sex and MMS flirting, as well as complicated gambling games, violent videogames, raunchy video-ringtones, porn clips and so on.

The Yankee Group reckons the global market for sexually-related wireless content could cross $1 billion by 2008. Projections that include gambling and violent videogames as part of wider adult content suggest this is a gross underestimate - the total market could be over $4 billion by 2008.

Providing profitable paid adult services on wireless is easier than on the web. For one, people are more prepared to pay. It's easier to reverse phone charges or to pay for a premium-charged SMS/ MMS service as part of a monthly bill than to reach for a credit card.

Most Euro-13 networks offer adult content and some, like the Italian Wind derive up to 80 per cent of revenues from sex channels and "date-and-flirt" services.

The explosion in adult wireless content has created new regulatory issues. Mobile penetration is far more widespread than the conventional Web. There are more minors wandering around with unsupervised mobiles. As networks and handsets upgrade, controlling access becomes more important.

The US is drafting a Video Voyeurism Prevention Act designed to make covert footage liable for prosecution. Every European government is considering measures to stop minors getting their hands easily on adult content. But legislation has to be translated into technically-feasible solutions.

Some handset manufacturers are working on solutions. Nokia is experimenting with a filter that bars access to services by content-category, price and file-transfer size. This is part of an "Intelligent Content Delivery" package designed to be implemented by service providers.

Service providers are also setting up handset-independent filters. All UK network operators are committed to putting filters in place by January 2005. Each network has its own definition of adult content without an independent regulator.

Vodafone implemented a blocker in July 2004 in its UK services. This is activated by default and can only be switched off by a user with valid age-proof. An early glitch led to users being blocked from email access.

Ireland is introducing an industry code of practice, a parental guide to mobile phone services and a mobile content filtering trial as part of its 3G initiative.

The German networks are offering optional SIM-cards that don't support adult content. France is wondering whether it can make service-providers liable for offensive content.

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