I'm sure with modern technology they can pinpoint someones mobile phone anywhere in the world
There are, particularly in such a relatively radio quiet zone as the Indian Ocean, however the people with that tech aren't going to show their hand. At best they might (if they have anything) communicate it to select members of the investigation or SAR teams via suitably obfuscated back channels (military SAR belonging to one of five nations might be simply directed to an appropriate place to start
though perhaps they might wait a little time if the outcome is self-evident, just to not make it too obvious). If the data were recorded it will probably take some time to mine it.
The find-my-phone type services will be useless here: next to no GPS signal in the cabin, very little chance of sufficient network interaction to get any sort of fix (handsets might start some sort of handshake but very little chance of data exchange; they will most likely assume they are still in KUL). Where the flight crossed the Malaysian peninsula there might be some logs of handset handshakes with a few cell base stations. If the aircraft ended up on the northern arc there could be others in other jurisdictions
if the handset batteries kept them powered for that long. However,
if the cabin was depressurised at altitude (could have been -40 degC) and the flight spent a lot of time out of cell base station range (the second factor almost certain) then the battery life will have been reduced. As mentioned before, trying to get those log details (if they exist and are recorded by the carriers concerned) from multiple carriers across different countries will take time, if it is possible at all.
and there were reports that some passengers mobiles were just ring ing out, why could they not use that technology to locate them?
That's been
covered repeatedly. The system will provide a ring tone whilst hunting for a handset so the caller doesn't hang up.
And surely you'd think the black box would have a GPS type signal in it, i suppose there are reasons why..
It does record navigational data from the aircraft. Lat/long are in there. Once it is disconnected from a (disrupted) aircraft clearly it's not going to receive any more data. No point attaching GPS to it as that would get destroyed in any land impact and there would likely be a crater/fire/smoke/casualties/witnesses aiding location anyway. GPS is useless underwater (no signal). Hence the use of an ultrasonic locator beacon.
Aircraft have an emergency locator beacon, ELT, (actually several) on board which will activate on land (triggered by accelerometer on impact) or on immersion in salt water - though that will only help if the ELT can float free of the wreckage (not sink with it) or be carried free by any survivor. There are of course impact scenarios where the ELT(s) may not survive to transmit.
