The Secret New York is a great idea of interactive sightseeing. There are several yellow arrows placed in NY with a phone number and a code. When you see one, you can call the number and type in the code. Then you hear a voice recording telling you all about this place and why it was worth for the yellow arrow.
The best thing about it: anyone can suggest arrow placements, for all sorts of reasons. On the website you can see the arrow placements and also the description. Sometimes, it’s even a short film clip about the place (I wonder, though, how you would use that feature on your mobile phone).
This in itself is a nice combo of web, mobile and real life. However, I think it won’t be long until this might be exploited by advertising or marketing:
1) Stick an arrow (whatever colour) to your shop door.
2) Users can then call up a number and listen to what other people said about your shop.
A community of shop (and/or product) reviewers like at shopping.com or others, only with shops in real life instead of online shops.