BBC broke the news yesterday (thanks to John for the tip): "Researchers from Mid Sweden University have constructed an interactive paper billboard that emits recorded sound in response to a user's touch. The prototype display uses conductive inks, which are sensitive to pressure, and printed speakers."
After some digging and struggling with Swedish (the ways one navigates pages in completely unfamiliar languages would make an interesting usability study), I fished out some details and links.
The "billboard", it seems, is part of this Paper IV project that's been going on at Mid Sweden University: "We believe that the technologies that will be developed initially will be of interest to popular magazines and newspapers, and we will focus our attention there to start with. However, we will also study, in parallel, the feasibility of implementing these technologies in billboards and product displays of various types." Here's a video showing the technology at work (the above picture is a screengrab of this). Also see some other related projects the group is working on.