In Belgium SN Brussels Airlines is currently running a very successful and funny campaign to promote its low fares for early bookings. Based on the idea that if you're early to pay less, Snow by LG&F; come up with a "wake-up call" idea.
As Jonathan Detavernier strategic partner at the agency explained me... "we created a wild postering and guerilla campaign that is now hanging in the major cities of Belgium. Those posters and street tags point to this website. On the site, you can check out how much a destination is. But you can also order a free 'wake up call' for a friend. You fill in the form on the site and choose a location. After that, you get a phone call: a voice asks you to leave a message for your friend. The next morning, your friend gets a wake up call: "Goodmorning ... just to say that you have to choose your friends a bit better. One of them asked me to wake you up" and so on. The message ends with: "Wait, I'll pass him through." Then you hear the voice of the friend that initiated the call."