Ask HN: Location based messaging service?

This is my first post. Does there exist a service where one can leave a message based on location? Twitter is obviously great for message passing and microblogging. Facebook and Google+ certainly help bring us together. I'd say that the combination of these two services greatly help communities all over the world exchange messages. Throughout very recent history, it was made abundantly clear that these technologies amplified many voices that needed to be heard.

Here is my question: Is there a service that allows for messaging based on location? Like Twitter, but with anonymity and coordinates.

There was a post on a 'Show HN' thread that seemed very close to implementing this idea, but didn't. That post pointed to http://rround.me. This project looks great and ended up getting quite a few people excited. However, it's not what I had in mind.

I've spent some time implementing this idea. After several iterations, I like my prototype. However, I know that this kind of application (if popular) would require a stronger backbone and would completely destroy my shared host. I thought this idea would be great to implement by myself so that one day I could show it off on HN, but I think that that day may be too far away. I've decided to try and lead a team for my final software engineering course to develop this idea. I wrote an article today detailing more aspects of the project as well as my concerns about sharing the idea. If you want, you can read it at http://cameronbriar.blogspot.com/2012/01/sharing-original-idea.html