http://www.ledauphine.com/haute-savoie/2012/02/16/avalanches-votre-iphone-pourrait-bientot-vous-sauver-la-vie reports an IPhone App that is currently being field tested in collaboration with the PGHM.
My rough translation of the important bit is
Operation is simple: once the application is downloaded, the iPhone works independently. Each time the skier stops, it analyzes the course before the stop. If it corresponds to an avalanche or a fall (whose characteristics will be pre-registered), it automatically sends an SOS message. Ideal if the victim is unconscious, when we know that in case of avalanche, the first fifteen minutes are vital. If conscious, it can also manually trigger the alert. This product is intended primarily for off-piste skiers.
“With my application, even if the skier does not know where he is, his phone does. And finally the language barrier: the laptop directly transmits the GPS coordinates to the rescue services. “
If the phone has no signal from a base station, The iPhone switches to Bluetooth and sends an SOS to all iPhones equipped with the application within a radius of 100 meters.
There are quotes from the PGHM underlining the obvious importance of achieving an extremely low false alarm rate (they ask for zero) and some other tricky areas. The Bluetooth mode sounds easier to implement robustly. The article suggests the app could be available in a month, but I suspect that more time will be neeeded for field testing and algorithm refinement.
I don’t know how accurate GPS in an iPhone is: the Wikipedia article http://en.wikipedia.org/wiki/Error_analysis_for_the_Global_Positioning_System
says 5m. If this is right, a GPS location would not replace a transceiver, but might speed up the initial search.