The announcement last week from Vodafone and Yahoo! that the pair plan to team up to advertise on UK mobile phones throws up some interesting questions. Not least of which is how to avoid annoying customers with what many will see as merely mobile spam.
As well as developing viable models and formats for sending and funding this advertising, the joint venture will need to spend time and money actually persuading customers to receive the advertising.
One option is to offer users a reduction on their monthly tariffs or the cost of their handsets in exchange for receiving the ads. Another is to offer free content, such as music videos, but with the caveat viewers must watch ads first.
Blake Chandlee, the director of UK media sales at Yahoo! UK and Ireland, says its plans are well developed: "After six months of research, we've established five or six viable business models we can use to draw consumers in."
Quite which method will grab the most customers is unclear, the medium is still in its infancy and there are no official take-up numbers.
Charlie Dobres, the deputy chairman and executive planning director at i-level, says: "Who knows where this will go? The end point could be people getting their phone and calls for free in return for advertising, paid for by the advertiser. That is where it is going, but this could change tomorrow."
So what and, crucially, who, will be advertising on mobiles if Vodafone and Yahoo! get their way?
Yahoo! has identified several possible revenue models from search and message alerts, through to sponsorship and traditional web advertising on a phone. Yahoo! is already working with a number of agencies, and even directly with some advertisers.
And Yahoo! is extremely keen to take collaboration seriously, arguing that a disciplined approach here will move the medium beyond text-based messages.
Mobile's personal nature is both a plus and a minus for advertising. While those involved in creating the ads are excited about the chance to talk to customers with highly tailored messages, they're aware anything intrusive can be ignored, or end up alienating the customer.
"More than any other medium, the customer is in control with mobile. This means it's going to be extremely easy to piss them off," Robert Campbell, the managing director at the production company Outsider, and a producer of mobile and viral content, warns
Mark Slade, the managing director of 4th Screen Advertising, a company that buys and sells media space on mobiles, believes that for the advertising to be successful, it has to be driven by original content, such as MTV's "mobisodes" - episodes of its programming developed especially for mobiles.
He says: "Enough people are using 3G now to get a critical mass of penetration."
So far, advertisers willing to invest in putting their brands on mobiles are small in number.
Sainsbury's offers branded recipes via SMS, while Leo Burnett shot a road safety campaign for the Department for Transport with mobile phone cameras, which was distributed on mobiles, as well as running on TV and cinema.
Such ads are just the start. As understanding of the medium grows, it will be a much bigger creative opportunity for agencies and advertisers - as long as they can avoid annoying their users in the process.
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DIGITAL MEDIA PLANNER - Charlie Dobres, deputy chairman, executive planning director, i-level
"Ads on mobile are already happening. Seventy-five per cent of texts sent are commercial - things like goal alerts. But how many of these get noticed, or even looked at? Advertisers are limited by what people will accept.
"For mobile advertising to be effective, someone needs to come in and do something original that will make people watch. The creative agencies may struggle with this, but digital agencies are well placed. They already know how to engage with an audience on their terms, which is vital.
"However, there is a lot of hype around this at the moment, and it's still very early days."
DIRECT MARKETING CHIEF - Simon Hall, founding partner, Hall Moore CHI
"Mobile's advantage is that the channel is something people already carry around with them - we just have to wait for them to start using it in a deeper way.
"The challenge is that it is such a personal medium, if it's handled clumsily it will alienate the audience. The creative opportunity is going to come from users creating their own content.
"A lot of clients are talking about it, but it's still at the bottom of the pile when it comes to budgeting at the moment. It's definitely one of tomorrow's problems, but it will start to gain significance in the next 12 to 18 months."
CREATIVE DIRECTOR - Graham Fink, creative director, M&C Saatchi
"This offers good creative agencies a real opportunity to make a massive impact on the consumer. It will also change the way we think because the medium is now the clever bit - it's not just about coming up with the creative idea, it's about finding and exploiting the right medium in the right way.
"Consumers are ready to pay attention if they are suitably reimbursed or paid - as long as the advertising is based on a good idea. Similarly, this applies to the client as well; many are interested, but it needs presenting in the right way if they are going to take it up."
CLIENT - Fiona Seymour, head of publicity and marketing, DfT
"While potentially powerful, mobile phone advertising's intimacy with the individual could be its undoing, since messages that are inappropriate will only serve to damage consumers' trust.
"Its effectiveness is dependent on a clear understanding of the audience and how it interacts with their phone. Our teenage road safety ad worked well.
"For the Government, using mobile phones as part of our campaigns needs to be carefully considered, not least since we can't be seen to be encouraging further mobile phone use among children. From a road safety perspective, we need to ensure the timing of the delivery is controlled in order to avoid dangerous distractions."