YellowPin has recently launched a simple social networking tool that lets your Facebook friends know where you are when you update via mobile. It explicitly doesn’t work with GPS, so folks only transmit their location when they want to, and aren’t perpetually checking over their shoulder for stalkers. It works by sending SMS commands like “pl valley view center, dallas, tx.” to 555888, which then updates your location for friends to see. Facebook is a solid start, and it’s entirely likely that YellowPin will spread out to other application-capable social networks in due time (Twitter, maybe?). Not a bad little service, and it only costs a dollar each month. Interested? Go ahead and take a look.