Digital has been stealing the headlines over the past few months for being the fastest-growing medium. But outdoor has quietly been doing very nicely too, making two of the few media showing revenue and share of revenue growth in an ever-fragmenting marketplace.
Not only do they stand out as two media in the ascendancy - both showing year-on-year growth for the past 18 consecutive quarters - but they have also struck up an interesting symbiotic relationship.
So what is the secret of success for the oldest and the youngest media, and what makes them work so well together?
One major factor in outdoor's success - constantly referred to by those working in the industry as the "last broadcast media" - is simply that people are now spending more time out of home.
James Copley, client development director at Kinetic, says: "This medium is growing because of how consumers are spending their lives: they spend 51% more time out of the home compared with 1995 and that's set to increase by a further 25% by 2012.
"People are spending more time out of home than in-home awake. This is a big structural change in society, so the audience is growing for outdoor media. It also generally tends to be an attractive audience for advertisers: upmarket and young. There has also been a huge investment in infrastructure of this media opportunity recently - better sites, illuminations, bigger signage - so the advertising is looking more attractive to advertisers."
It is digital technology that has catapulted outdoor from its most basic paper, glue and paste brush image, to a medium that can rival any with its immediacy and mastery. Digital technology means outdoor sites are no longer fixed for week- long or longer periods. Advertising messages can be altered depending on the time of day or location, among other things. Moving images can create a dynamic and eye-catching ad in numerous locations and work especially well in stations and spots where dwell time is longer.
And developments such as Bluetooth, Global Positioning System (GPS) and quick response (QR) codes allow consumers to interact with outdoor sites in a way that they've never been able to before.
Peter Charlton, sales director for CBS Outdoor, says: "There is an opportunity to use interaction. GPS technology is getting us to realise what's available at a location. LED screens on 25 London buses could change the message depending on where the bus is."
But it is Bluetooth that has really got everyone talking. To some it is the future of outdoor, while to others it is an overblown distraction. How the consumer views it seems to depend largely on age. The M-generation, which has grown up with mobile and has no recollection of life without it, is more than happy to be Bluetooth active. However, for many older consumers, it is less welcome.
"Half the battle is to get consumers to turn the Bluetooth function on - there's a marketing job to be done there in itself," says CBS's Charlton.
"It's just naivety. If it becomes intrusive, you can turn it off; it's about finding the right time to interrupt us. But we will see more and more of it."
Damian Cox, managing director of Ocean, is a Bluetooth convert. "It's fantastic; it's like being a child again and being excited about getting a letter through the post," he enthuses. "It's not mainstream, but it's an exciting addition for clients to have."
One of Ocean's Bluetooth campaigns was for Diesel at Centre Point in London. During a two- week period, the site detected more than 63,000 unique devices and recorded a response rate of 2.3%. Those that responded received a short film of two women and a man having a pillow fight clothed only in Diesel underwear.
Whether the Diesel download fits the criteria of engaging content is a matter of personal taste, but this is what many in the industry identify as being necessary for success.
Pete Beeney, group head of Titan+Digital, advises: "The first people to really crack it will need to treat it like online treats virals; as a free-to-share media. It will have to be content-driven, something people really want on their phone and want to show to others."
But some at Titan are cautious about the technology. While Beeney refers to technological restrictions on how many phones can be sent content at once, his colleague, managing director Andy Moug, is similarly guarded against over-hype.
"We still think Bluetooth might be niche," he admits. "It has to have something that people can engage with, something they can use or laugh at, not an advertising message.
"With clients and agencies, I get the sense that they have had the media owners talking lots about it, but question what it's delivering. What is there out there that's actually working?"
Moug is a big advocate of the school of thought that "just because you can, doesn't mean you should" - something Dominic Gesua, sales director at Blowup Media, agrees with.
"With Bluetooth, advertisers have to be careful not to take it beyond the consumer; it's good, but how many people use it?" he argues. "You cannot ram technology down people's throats and lots of people don't have it switched on."
But it's not just with Bluetooth that outdoor and mobile really engage. With the rise in mobile devices - estimates suggest there are nine times more mobile devices than PCs in the UK now - and the advent of short code texts, outdoor can stimulate immediate interaction with consumers.
And the technology is advancing all the time. QR codes are 2-D visual barcodes first developed in Japan in 2002. People can take a picture of the code from a poster with their mobile, which then automatically opens up a mobile web page with further information.
Last month saw the first poster making use of this technology launch in the UK. Forming part of 20th Century Fox's DVD release of 28 Weeks Later, the poster was sited at London's flagship HMV store on Oxford Street. If shoppers scanned the code with their mobiles, it took them to a secret URL that linked to exclusive content from the film.
Simon Wardell, head of Create at Clear Channel Outdoor, which worked with Fox to develop this site, says: "We're constantly looking at new ways of enabling advertisers to interact and engage with consumers. The QR code opens up new avenues for interactivity and can be adapted for campaigns across all industries."
In Japan, where more people surf the internet with their mobile phones than PCs, QR codes are growing in popularity. While they are only just appearing in the UK and media owners are still unveiling digitised outdoor sites around the UK, this is very much a work in progress.
However, the one location that has the industry buzzing, as it is a rare example of a site that has not had to be retro-fitted, is Heathrow Terminal 5. The new construction means BAA and JCDecaux Airport, which has invested £20m in it, are showcasing the next generation in terms of outdoor. The locations have been built into the design to achieve maximum impact from the start.
Richard Malton, marketing director of JCDecaux Airport, says: "When Terminal 5 opens on 27 March, we'll get critical mass in one hit: 200 screens will be switched on in one day. This isn't a gradual thing - it's part of the development and digital was a key driver in the interiors of Terminal 5."
Malton says the quarter of a mile-long retail walkway, with screens running the length, will be the best retail environment for advertisers in London. "This is a closed environment where digital works best. People are sitting there for two hours and there are no restrictions like the Highway Acts, so you can really engage with the audience."
The sites aren't automatically Bluetooth-enabled, although they will be able to run campaigns using it. "Bluetooth isn't in there and the jury's still out," explains Malton. "We recognise that it gives advertisers the chance to broaden and engage more. But Terminal 5 is a very precious asset and we don't want passengers to be too bamboozled.
"So our policy is to only ever have one Bluetooth campaign at a time, to stop the 'piss off' factor for the effectiveness of clients."
But there is also a very simple relationship at the heart of the digital and outdoor push. For the ever-growing list of dotcom companies establishing online businesses, they need a "shop window" to advertise their wares and outdoor fits perfectly. It gives the companies a means of talking to their customers they cannot gain online.
Kinetic's Copley says: "Because they are virtual businesses, they see poster signage of brands as their retail space. Companies such as Lastminute and Expedia are big outdoor spenders, as they need real life concrete branding. As they become more homogenous, they also need it to differentiate themselves from their competitors."
Outdoor advertising campaigns are used by digital companies to encourage branded search rather than generic search.
The IPA's Touchpoints research shows that spikes in internet action are after travel to and from work, with most activity first thing in the morning and also in the evening. And consumers are now more than familiar with seeing web addresses on posters and are, in the main, as comfortable with them as phone numbers, especially among the younger audiences.
David McEvoy, JCDecaux's marketing director, sums up the symbiotic relationship thus: "The internet gives you the detail, the fulfilment, but it lacks the brand building. Use a poster to say the event is happening or a new brand is being launched, and then drive the audience to the internet for the detail. It is the best of both worlds."
Brief: To launch T-Mobile's Mobile Jukebox service and position the new W880i Walkman phone as the "hero" Mobile Jukebox handset. The strategy was to combine traditional and interactive media and give the public the chance to experience the usability and functionality of the handset and service. The service allows users to download tracks for £1 each.
Budget: Not revealed, but it was described as "an important campaign".
Creative: The idea for the campaign was created by Iris and developed with Kinetic and JCDecaux Innovate. It was inspired by a campaign that the company had done in 2005 for the first Walkman phone.
The fully wrapped interactive bus stops were designed to look like a park scene including grass-like vinyl on the floor and clouds on the ceiling. People sitting waiting at the bus stop looked like they were sitting on a park bench. Craig MacLennan, marketing manager UK and Ireland at Sony Ericsson, says: "This was representing the essence of the campaign 'Music where you're at' - wherever you are, you can download full track music from T-Mobile's Mobile Jukebox."
The interactive panel featured a larger-than- life phone with a touch screen. Passers-by could select tracks and listen by plugging in either standard headphones or through a fast-port connector for existing Sony Ericsson customers.
"The core above-the-line campaign creative was themed around 'moments' - where and when the customer would be most likely to use the W880i and Mobile Jukebox service - on the move and out of home," adds MacLennan.
Campaign It ran for four weeks in July 2007. As well as the five interactive bus stops, it included nationwide six-sheet posters, online executions, bar dominations including runners and beer mats (using the line "Make mine a single"), press advertising and sponsorship of the Metro newspapers' chart.
Measurement There was an increase in Mobile Jukebox active users and downloads. Footfall to T-Mobile retail stores increased in most regions and sales conversion rates also went up. There was high engagement with the bus shelter activity. Over the whole campaign, there were almost 120,000 interactions, with a site daily average of 427, according to JCDecaux. A total of 47,000 tracks were downloaded from the touch screens.