I don't know Hempy. I though I had read ages back that Vietnam saw them turn back to Malaysia, and they had told the Malaysians. I don't know if this means they told them in real time, or only later when everyone realised it had gone missing. Not sure anyone knows given the way so may things have been stated one day and then revised the next.
People here have said they heard HCM trying to contact them. I think also the other MH flight was asked to try to raise them.