The OOH campaign for the Google Voice mobile search app in the UK includes billboards with pronunciations of London Underground tube stops as well as things people search for on their mobile while out and about:
Taxi Numbers (tak-see num-buhz)
Travel Updates (trah-vuhl up-deyts)
Some Google adverts along the Tube included:
Leicester Square (les-tuh skwair)
Oxford Circus (oks-fuhd sur-khus)
Piccadilly Circus (pih-ka di-lee sur-khus)
The billboards get your attention because of its minimalistic design and the fact it's just a bunch of gobbledygook thrown on a wall. The tag "say it to get it," instructs the viewer to say it out loud, and it does take a few seconds to figure out the ad. But it doesn't take too long where the viewer starts to lose interest. Figuring out what the ad says is an interactive game in a sense.