Cellphones only work within 4000' above ground level.
Anyone who doubts the danger of lack of oxygen and it's creeping effects, should do a session in a decompression chamber. I've witnessed people, so "drunk" from lack of Oxygen, they were incapable of putting a mask on, leave alone being incapable of writing their own name.
If decompression was the case in this disaster, then they all may have just gone to sleep. There are worse ways to go out.