A couple of mobile campaigns i've loved recently. First one is "Ringtowns", from Ogilvy Guatemala and their client Claro, using ringtones as a device of spreading the service itself, naming them after all the cities in the country (click the image to see the video explaining the case):

The other one is "Os Ringtonicos" ("The Ringtonics"), from Almap BBDO for an NGO called "Casa do Zezinho", whose kids recorded ringtones using their voices to raise money for buying musical instruments:

Like them because they're so human, using mobility as a tool instead of just as a channel.