Siemens recently announced the digital graffiti service they’ve been working on for a while:

Post-its are exceedingly practical. They’re a handy way of letting people know if you’ve gone out quickly to shop or to lunch, or for reminding you to do things. However, you can’t stick these yellow memos in mid-air – at least not yet. But that will be possible in future with the virtual post-its from Siemens Corporate Technology’s research laboratory in Munich. Dieter Kolb’s team of specialists have developed computer programs that assign cell phone messages to specific locations. The user can leave a message, known as a digital graffito, at any geographical point. This is a kind of SMS attached to one spot. When the recipient reaches the defined point, the message appears on his or her display. Unlike the classic SMS, the message is not sent to the addressee as such, but is only activated when the addressee comes within a defined radius of the location specified for the graffito. Another difference is that, if required, the message can be read not only by one person but also by a number of cell phone users – like a real graffito plastered on a building wall. This allows a whole range of new applications, for example for special offers and advertising messages aimed at a large readership, or for making arrangements with friends.

As Warren Ellis says, this “obviously has just hideous possibilities for advertising. But the potential for art is also pretty impressive.” I agree with him and am trying to be optimistic but as the amount of spam I get in my email and on my blogs keeps on increasing I’m beginning to wonder if, you know, no one can have nice things for very long anymore.
Related (cellphone-based and to do with physical location) projects from my fellow ITP kids, off the top of my head: John Geraci’s Grafedia, Ian Curry’s Bluefish, Dennis Crowley & Co’s Conqwest, Elliott Malkin’s proposal for eRuv.
Also one of my ideas for a future iteration of 24in48 was that when people’s cellphones can send location metadata along with the MMS, it would be neat to have one of the viewing interfaces be a map of the city, updating live with the location of the photos as they arrive. Clay Shirky‘s suggestion was to see if I could tie into the Dodgeball database somehow since it stores lat/long coordinates, but that would require people logging into Dodgeball every time they move somewhere different—and there are already too many keypresses involved in moblogging for the average person. Hardware manufacturers need to get it down to just two clicks: the first to take the photo and the second to send it to a preferred email address.
(With a third to send it to any other address from your address book, of course. An informal survey of my friends who moblog suggests that long tail is at work; many of us have Flickr saved as “* Flickr” in our address books, since it’s what we send our cameraphone photos to 99% of the time and having the asterisk puts it at the top of the list and saves us the time and energy of scrolling down to find it each time. Kathryn and Matt‘s s700i phones are halfway there: they pop up a list of the last five addresses you’ve sent photos to. Which is good but not quite good enough!)