I just read another story where two people got stuck in the snow in a remote area in the Sierra Nevada mountains without cell phone service. They were reported missing two days after they got stuck. Paula Lane was found after 6 days by her brother who didn't give up after the official search was suspended. But unfortunately her boy friend did not survive. Over the years I have heard of other tragedies like this where folks got lost in remote areas but had their cell phones.
My suggestion is that the search and rescue team simply deploy portable cell phone towers and continually ping/call their cell phone numbers or listen for their calls, in addition to the traditional S&R.
The basic technology already exists. There are portable towers (http://en.wikipedia.org/wiki/Cell_on_wheels) that could be driven along the suspected route the missing folks took. If the search area is large, the tower could even be designed to be suspended from a helicopter to increase the range. There are portable towers that appear to be small enough for this (http://www.survivalistboards.com/showthread.php?t=166036).
S&R teams could find out which phone provider the missing person used and use the appropriate portable tower.
With proper publicity in high risk areas (esp. snowy, mountainous or wooded), missing persons with phones would learn to stay with their cars/chargers, or preserve their phone battery power as much as possible. They might even be located by GPS when their phone gets in range of the mobile tower.
Hopefully in this way, with some tweaking, some of these tragedies can be avoided.