"Can anyone explain the phones ringing out? Which I presume means they must be intact?"
Yes - a mobile phone sends out a signal to the cellphone tower to keep in touch. Each tower us at the centre of a cell and each cell is about 35km across. Sometimes it can take a few seconds for the cell tower to id where a phone is. In that time, so that the caller doesn't lose patience and ring off, the caller will get the ringing tone. It actually happens all the time - just because the phone rings at the dialler's end doesn't mean it's actually connected.
This crash is a super-mystery right now and it's clear the Malaysian authorities aren't telling us everything.
I work for an aeroplane builder and I have a degree in aeronautical engineering so I'm watching this with a lot of interest. It is a bit strange not to have found debris near where they have been saying the aeroplane is located. Lots of aeroplane parts float from the fin to seat cushions. You would expect that they would have found something if it went down where they thought it did.
Latest information is that a military radar seems to have tracked the aircraft flying in the opposite direction, on the other side of Malaysia peninsula more than an hours' flying time from where it should be. I wouldn't want to guess exactly what's gone on here. In the industry the main speculation is around hijacking and/or bomb detonation. There are other theories that relate to major structural failure - but in that case we would have expected ACARS data to be transmitted from the aeroplane to a satellite (the aeroplane in question was involved in an incident that severely damaged its wingtip. If the repair failed in flight it can trigger 'flutter' - extreme vibration of the wing as the air flows over it - that can break a wing off). ACARS is a maintenance system that monitors the 'health' of the aeroplane and sends the information to the airline in real time. The Malaysian investigators yesterday said that they are not releasing the ACARS data - which I find suss. Another speculation is that the crew became incapacitated by a leak of air at high altitude that triggered hypoxia and the flight crew passed out. If it's this, then they will probably never find the plane. It had enough fuel for a 7 hour flight plus enough fuel to divert to an airport 200 miles away and hold over the airport for 30 minutes. So let's say 8 hours x 500 miles per hour - it could be the best part of 4000 miles from where they think it is. This has happened one to a private jet and once to an airliner - but never to an aircraft of this size with this much fuel on board. But you'd expect that a radar, somewhere, would have seen it and the aircraft's tracking device (called ADS-B) would have been traceable.
It's all weird and there has to be a certain amount of info not being released or they'd have found it. When AF447 crashed in the middle of the Atlantic, first wreckage was found 48 hours later and much more 5 days later. The Atlantic's a hell of a lot bigger than the area they're searching now!
Sorry - just trying to succinctly describe some of the main possibilities we're discussing inside the aviation industry! And it's all speculation.