I use the Lightspeed Zulu2s and find that they deal very well with prioritising what calls, basically anything that comes through the Aux input (Aka, your normal 3.5" input) or through the Bluetooth is automatically reduced to 20% of its current set volume and is done so quickly that i've personally never missed the start of any call!!
Jas24zzk, personally when i'm fly VFR (Which is mostly for scenics) I don't get the punters to turn them off, as its never caused me any problems, not even when searching for signal or anything like that coming through the headset. IFR is a different story, I like to play that one safe and require all mobiles to be turned off completely.
What a lot of people don't realise though about their Headsets is that when your comms go dead the Mobile Bluetooth connection no longer works, in some, in the Lightspeed Zulu2 you actually have to change one of the setting pins inside the battery compartment for them to work whilst "Unplugged".