MEDIA: STRATEGY OF THE WEEK - BT DIRECTORY ENQUIRIES. Giant yellow Post Its adorn thousands of sites all over the nation

So, it's the moment of truth: 192 has been sent firmly into retirement.

Time to see what effect those moustachioed joggers, banjo-playing fools and strange comic-strip legs have had on an apathetic British public.

The latest campaign to cause a stir is BT's offering from St Luke's, which has waited until the very last moment to unleash its full force on the nation by covering it in Post It Notes.

"The biggest debate was always about when to launch," says Donna Glanvill, the media director at Rocket, which works with BT on its media strategy.

"It is a very low interest category and the average person is not fascinated by it."

Also, because most people dislike change, the public has no motivation to take notice of the new numbers until they have to. Figures issued from BT in May showed that only 53 per cent of people were aware of a number change even though The Number's 118 118 and Conduit's 11 88 88 had been advertising since March.

BT's strategy sprang from trying to think like the uninterested and wary consumer. It recognised how people are confused by the range of numbers and guessed they would ignore the advertising while 192 was still operating.

The crucial part of BT's strategy has been to bide its time and wait for the week prior to the switch-off date when people were forced to change.

Kate Morse, an account director at St Luke's, says: "It makes sense to invest your spend when the issue is at the front of the consumer's mind." The aim was then to launch big with a campaign using all available media with the exception of radio. BT believes that this will maximise the effect of its £10 million budget.

The creative idea behind the campaign was simplicity and accessibility.

With BT's target market being the huge "all adults" category, it was important to use an idea that every generation could identify with. The traditional BT branding was retained as something all age groups recognise and also to give the campaign credibility. "We wanted to be very, very clear about which number is coming from BT and that this is the one worth remembering," Morse says.

On 14 August, a week before 192's shut-down, BT launched the 118 500 Post It Note campaign. The first burst came on TV in two-second "blipverts" bought by The Allmond Partnership. These were expanded on and explained in 40-second ads in primetime viewing on Sunday 17 August. The ads showed Post It Notes with 118 500 scrawled across them in locations across the country and urged people to "make a note" of the new BT directory enquires number.

Although the campaign became outdoor led, television advertising was used to provide national reach. "It would be physically impossible to put Post It Notes across the whole country but the TV ads work with the outdoor activity, implying they are everywhere," Morse says.

The outdoor work, bought by Outdoor Connection, was placed on the day of the television launch and focused on four major UK cities: London, Manchester, Glasgow and Birmingham. These areas were chosen because of their concentration of 16- to 35-year-old "social actives", the key demographic within the target market. Post It Notes were stuck all over the four cities on 15,000 poster sites. There were also various special-build sites holding giant fibreglass Post It Notes and five megasites with Notes ranging from seven square metres to 15 square metres. Rocket saw this outdoor focus as the only option given that the campaign idea surrounded Post It Notes. Morse says: "Post Its can only be brought to life in the outdoor medium."

The campaign also made use of ambient media and door drops, with 100 million individual Post It Notes stuck on to front doors, pizza boxes and take-away bags and inserted into newspapers and magazines such as Time Out. Ogilvy One arranged the door drops, Outdoor Connection bought the ambient media and Starcom bought the press.

BT's campaign differs to those of the other contenders but it remains to be seen whether it will deliver. Glanvill is convinced that BT has it spot on. "We have the right approach and are confident it will be a success," he says.