Teslinhiker - I have used Sat phones myself. The rates for intl. calls are quite expensive. But they are good in the sense that calls from remote continents back to home base (USA or UK) are quite clear.

There are also companies that offer "apps" for local cell phones - with the intention of sending out an alert that people have a crisis.

Both of these technologies fail during a violent kidnapping. The kidnappers are rough, they move fast, the victims are banged up, and their phones are confiscated. Kidnappers always remember to take their victims phones during the early moments of an abduction. So the phone link to the victim is lost almost immediately. However, a small secret GPS tracker might escape their attention for a while longer.

Pete