Looks like there's another location-based digital graffiti project - Rixome. Here's the blurb from near near future:
"rixome is a network and a tool that turns mobile screens into windows that show the virtual and public dimensions of our point of view.What I'd really love to know is, when will there be something like this available in New Zealand, and will it be just a short-term research project, or will it be ongoing? Hopefully the latter!
A walker (a rixome user) can see on his/her mobile phone/PDA/laptop screen the virtual interventions that have been added to the location where s/he now stands. For example, a spoken message can be left on a given location for other "walkers" to hear through headphones whenever they pass by. The message can also be written, or it can be a 3D animation or image, a photography, a drawing, a video."