You'd have to be living on Sue Lawley's mythical desert island to be unaware of digital radio. Even if you're one of the many millions of Britons without a DAB (Digital Audio Broadcasting) set, you can't have missed the trials that are pumped out daily by the BBC both on radio and TV.
And it's certainly difficult not to get enthused about the prospect that it offers. Alongside the better quality sound, there will be more stations offering a wider variety of music and programming than is currently available in the analogue world.
There are new niche offerings such as Passion for the Planet, a mix of environmental news and world music, AbracaDABra, a station for pre-school children as well as Smash Hits radio, for those who want non-stop pop.
It has also enabled stations currently restricted to certain cities to spread their wings and look for new homes across the country. Kiss FM is quasi-national on digital radio while Jazz FM has a much greater reach than its London and north-west analogue licences allow.
All these extra airwaves offer a great prospect for radio-based PR, you would think. Such campaigns will be able to get their messages out through more outlets, and by being more targeted potentially face less wastage.
However, digital station audiences are not yet measured, which creates problems for a PR campaign.
Given that the time taken to target a story at an individual station is the same whether the listenership is in the millions or the thousands, it's rare for niche stations to make the target list. 'I would advise clients that (digital radio) was an add-on to the other opportunities,' says Firefly head of broadcast services Keren Haynes. Few PROs in-house or at agencies will admit to specifically targeting these stations.
'I think our clients have only heard of digital stations that you can also hear on FM and AM,' she says.
Managing director of radio specialist agency agency USP Rob Jones agrees: 'PR companies have got to tread very carefully. They can put a promotional message onto (digital radio) but it may be that only 12 people hear it,' he says. 'At this stage you can't turn around to your client and say we've delivered a PR message to a large number of people because that's a lie.'
Nevertheless it may be a good time to forge relationships with some of these new stations, while they're still small. The real opportunity is to become an early adopter.
'How often do you get the opportunity to be involved with a media owner at launch?' says Markettiers 4DC managing director Howard Kosky. 'Stations do not forget. As a producer or programmer you are very aware of those people that assisted in the early days.'
However, even if digital radio forms only a minor part of a campaign, companies will still want to know the total reach of their activity.
The only problem is that it's difficult to know who is actually listening to these stations. Although digital sets can now be bought for less than £100 and were the "must-have" present this Christmas (with reports of every one of the 75,000 sets available in the UK for £99 sold out), there are still less than 150,000 in circulation.
But there is hope for increased listenership beyond the sale of cheap sets. From January, Ford also started offering in-car digital radios through its dealer network, an environment that many believe will ultimately be key to increasing take-up.
The hope is that by the end of the year many more sets will have been sold, giving a total audience of more than one million via DAB. 'By the end of the year when we are looking at, fingers crossed, 500,000 more sets, we are looking at a whole different ball game,' says Digital Radio Development Board press and publicity manager Mandy Green.
The situation is complicated by the fact that some digital radio stations not only broadcast using DAB but they also broadcast via digital TV or via the internet.
Stations such as OneWord, a national digital station broadcasting plays and books, gain access to nearly seven million homes thanks to carriage on SkyDigital, which has 54 stations. Cable TV also has a radio offering.
Official figures suggest that 14.6 per cent of UK adults have listened to the radio via their TV set.
Add in the problems of accounting for online listening - although audited web figures can help here - and you've got a tricky problem if you want to provide some accurate feedback on the number of people who've been exposed to your campaign.
The official radio audience figures from Rajar (Radio Joint Audience Research) - expected at the end of the first quarter of this year - will fill in some gaping holes in the digital listening landscape. Smash Hits, Kerrang! - which is broadcast on digital terrestrial TV - and OneWord have all signed up in record numbers to have their listening figures monitored.
These are expected to be available at the end of April.
Jazz FM, Kiss and the BBC Asian Network will also provide a total UK listening figure from the first quarter. This will be in addition to the analogue regional numbers that they already report and will enable web, digital TV and digital radio listening to be evaluated.
'We'll have a lot more stations signing up by the end of the year,' promises Green. This will provide a broader picture of digital radio listening, and he adds that the increased number of sets in the market and the rise in digital listening will make it more worthwhile for radio groups to pay for monitoring.
'I think by the time we get to the end of this year, digital will be part of Rajar across the board,' agrees UBC Media Group chief executive Simon Cole.
But there are ways around some of the loopholes in figures that provide a picture of the digital listening public. It is already possible to discover which stations are most popular with SkyDigital viewers. Research company Continental Research's specialist study provides a measure of reach for stations, via a panel of viewers/listeners.
A new set of data is expected shortly, but figures from the first results released last summer showed, not surprisingly, the top seven stations - Radio 1, BBC Radio 2, BBC Radio 5 Live, Classic Gold, Capital Gold, TalkSport and Virgin, all of which recorded audiences of above 500,000 - also broadcast on analogue.
However, Planet Rock - broadcast nationally on DAB - Total Rock - broadcast on the web and digital TV - and The Mix broadcast online and on digital TV - had a digital TV listenership of 250,000-499,999. Twelve more digital-only stations came in at between 100,000 and 249,999.
Once stations sign up to be included in Rajar's reports, this should also take into account most of this non-traditional radio listening, such as digital TV and web listening as the diary-based survey does not specify the form of broadcasting.
Cole says that with One Word attracting 60,000-100,000 listeners weekly on SkyDigital, that ought to be reflected when the first official figures are published in April.
Another potential way around this dearth of data is to look at linking any digital radio activity with promotions or prize-based competitions.
'At this stage, to deliver any kind of results you are going to have to put some response mechanism in,' says Jones. 'The station would run some sort of competition or voucher system. Then you can measure (response rates).'
Even if promotions don't suit the communications strategy, it is likely that the station itself will have some data on response rates from SMS messaging, for example.
Jones says Total Rock, which broadcasts on digital satellite, is one station that can go down this route.
'They do not have definitive figures but they have given us comfort and they have shown us responses to competitions,' he says.
Cole points out that PRs could also use any content they supply to digital radio stations to leverage better coverage on the more widely listened to analogue stations.
'In terms of PR opportunities, I think it's quite fair to look for trade-offs. Everyone's looking for content so if PR companies have got useful content, that will be well received,' he says.
In any case the early days of digital radio could be an ideal time to learn about how radio may soon be a very different medium.
Kosky says PRs will need to work hard to improve their understanding of the radio market as digital gets established. 'The measurement of how you look at radio moving forward on digital is very, very different.
It's about targeting,' he says.
'PRs need to be preparing their clients for the time when they need to be wanting to get on niche channels,' adds Cole, pointing out that 100,000 book buying listeners for OneWord is a very attractive prospect.
In this scenario, once digital radio is established, planning a broadcast PR campaign will become increasingly similar to planning an ad campaign.
'There's going to be more opportunity for more specialist radio programmes in the same way that the magazine industry has been able to provide consumers with every type of magazine,' says chief executive of entertainment and media agency Braben Company Sarah Braben.
Ultimately, digital radio is expected to become an important part of the media landscape, judging by the vast array of new stations launching and the encouraging sales of digital radios. However, while some niche audiences may become attractive targets quite quickly it will take time before the mass audience migrates from analogue.
'It's going to be the same as digital TV and ultimately as you get consumer buy-in so there will be more channels available and more audience to reach,' says Braben.
As those audiences grow and are measured, the digital radio audience is likely to prove a powerful, targeted group as each station carves out its listenership.
SEVEN SEAS EYES DIGITAL AUDIENCE
Seven Seas brand NeutraTaste is a taste-free cod liver oil, and like other cod liver oils, is a therapy for arthritis.
Arthritis Awareness Week (4-11 January) was an opportunity to promote the benefits of cod liver oil. The radio campaign would give advice to a broad audience of arthritis sufferers in the UK and Ireland.
Working with Weber Shandwick, Markettiers 4DC teamed up with the Arthritis Research Campaign and cod liver oil researcher Professor Bruce Caterson of the University of Cardiff to develop an editorial-led proposition for radio.
ARC press officer Jane Tadman and Prof Caterson fronted the campaign going out on 7 January.
As well as a host of analogue local stations it targeted national digital radio station Saga Radio. Aimed at an older audience, Saga would provide a highly targeted group of potential arthritis suffers or friends of sufferers.
Evaluating audience reach with Saga Radio is difficult, as Rajar does not yet measure its listenership. But the audience fit with the message, along with the quality production, ensured it made the target list.
Seven Seas cod liver oil marketing manager Tim Horne says the company is happy with the results: 'All participants recently benefited from some fantastic live coverage.'.