Given the low strength of Bluetooth compared to WIFI and that given you can use your WIFI enabled device on flightmode to access Qantas Entertainment or Qantas WIFI there cannot be a logical reason to ban Bluetooth at any stage of a flight.

Personally I have felt that if a mobile phones in normal mode could really interfere with signals to or from an aircraft or alter the avionics that the flight crew used surely they would not be allowed on board under any circumstances and we would be body scanned to ensure we did not conceal them and take them on board. To suggest otherwise I have felt is ludicrous and I am sure I will be flamed if there is evidence they can actually affect the safety of an aircraft. However I have formed my view that it is a dubious and mythical risk mitigation process for airlines, CASA and its like around the world to rely on passengers (sometimes up to 500) to voluntarily switch them to flight mode to ensure the safety of the aircraft - this would be prone to failure.