This is the first API that I've encountered that works with cellphone numbers. I can see this being integrated into Android for incoming calls from unknown cellphone numbers.
Also, there are many applications in the market that does exactly this. I haven't installed any of them since I basically don't trust anyone with "read/write contacts" and "full internet access" at the same time (perfectly valid permissions for apps like this, but that doesn't mean I trust them).
A search for "vemringde" gives you four apps that targets Sweden specifically (so they are probably quite useless outside of Sweden), one of them mentions that it only works while having a 3G connection.