It is simply kind of external, autonomous satellite mobile phone with included GPS attached to whatever part of the plane is most easily adapted for that purpose.
Yes, that is what ELT/EPIRBs do (but not sat phone). The newer 406 MHz units include a GPS and can transmit lat-long and have higher accuracy than the 121/406 beacons but in this case a beacon would be "good enough" to find the a/c I'd imagine. If the ELT had been activated and received we would have heard about it early on.
The issue is building something that can survive an impact and not be dragged to the bottom.
PS the postings about A319 electrical issues and A300 rudder breaking off aren't really as relevant as the ADIRU/pitch-up, WX and terrorism discussions.
Someone asked this and I didn't see an answer, does the AF A330-200 have the same make/version ADIRU as the QF A330-300?