The mobile screen may well become a primary medium for advertising, and it's not too soon for marketers to begin considering how they might best make use of it, according to a new report by media-buying firm Magna Global, writes MediaPost. Cell phones are likely to provide the greatest opportunity, with more than 2 billion users globally, 236 million of them with 3G service enabling video playback. "With a potential audience in the billions…this vast untapped market will ultimately emerge as one of the most important of the early 21st century," the report prognosticates.

However, the mobile video market is still relatively small, in part because of a dearth of content, the cost of handsets and subscription, as well as the lack of a proper infrastructure. For now, text messaging and ring tones remain the "killer apps" on cell phones, according to Magna Global.

Devices such as the Sony PSP and Apple iPod, as well as those that allow "place-shifting," (remote access to home cable and satellite services) such as SlingBox, are forecast to provide fewer marketing options.