According to a recent patent filing, Apple has considered implementing security that allows an iPhone to automatically contact authorities when stolen.
The patent application describes a system in which the user can set thresholds of vibration and acceleration (I assume to mark if someone stole your purse or something). If the predetermined threshold is met, the iPhone will lock down to block unauthorised use. In addition, the iPhone could send a message to authorities with embedded GPS coordinates.
Obviously this description is a big picture view of how the system would work, not exactly perfect for real world use (vibration seems like the most problematic possible way to measure if a device is stolen). But it'd be an interesting idea if tweaked a bit. [AppleInsider]