That makes more sense. You through me when you mentioned PLB.
I havent seen Sat Track 24, but I have seen a similar system locally which uses either the GSM or CDMA phone system.
Basically its a car alarm or fleet tracking controler that transmits a GPS location back to a control centre. The Sat Track 24 has the advantage of being able to connect a computer to the system, and also that it uses the a Sat Phone system. The extra features just seem like a value added bonus to these other systems.
I would look to the car alarm industry and fleet control tracking industry, and see what value added features they offer over there.

I think one of the reasons this system was designed is because the rental car companies has started to take the EPIRB/PLB's out of their cars. They were getting tourists 1000's of kilometers from anywhere setting them off over something simple like a flat tyre, expecting someone to come out and change it for them. The authorities started to crack the s^%ts and the rental companies removed the beacons.