Outdoor advertising used to be a one-way medium, but now billboards can actually connect with the cell phones of nearby pedestrians, allowing them to download music, ads or video clips. The bluetooth technology currently being used doesn’t work with cars driving by, and many of the initial implementations are in mass transit centers.

WSJ.com: CBS Touts New Shows in Video Clips, 2006-Aug-24, by Emily Steel

Like the addition of neon lights and three-dimensional fiberglass extensions to billboards, the marrying of mobile devices with outdoor advertising is yet another flourish in the booming outdoor-ad business. … "This is a way to take the message off the billboard and literally place it in people’s hands and into their lives," says Stephen Freitas, chief marketing officer for the Outdoor Advertising Association of America.