RE: GPS and cell phones
All cell phones and cell phone systems are now supposed to have GPS
capability BUT all the GPS capable phones I have seen also have the option
to turn the GPS signal off except for 911 calls.  And a cell phone can only
be tracked if it is turned on.
But a cell phone only works if it has a connection to a cell antenna.  In
the case of the Kims they had no connection. But their phone did receive a
text message and acknowledged that, refereed to as a 'ping' by those that
hunted through records and found the record of that signal.  That put the
searchers in the right area.  Prior to that the search was many miles away.