I found various applications that use text message that work like friend finders. All of them are very similar. This one I chose, Proxidating, uses bluetooth to warn the user when someone that fits her/his profile is close. It's a dating service and it's available in different countries. The users have to download an application and install on their cell phones.

www.proxidating.com

I also found this page that lists a lot of different mobile applications:

http://www.elasticspace.com/2004/06/mobile-social-software