I like the ideas below and everyone can agree that a PLB is always good to have, but most will not go that route. However, since they have a cell signal, a GPS with a baro altimeter such as the Garmin Geko 301, along with the cell phone they already have would allow them to send pretty decent (<20') location with elevation/altitude via text message. Then instead of T-Mobile trying to triangulate their location, SAR could concentrate on how to get to them. The Geko weighs all of 3.4 oz' so there is very little weight impact.