In the Airline i work for, it's compulsory to use the headset up to the TOC and from TOD to landing... Nontheless many pilots take them off above 10.000ft. Every time we use the headset, we do it with the INT/RAD switch in the INT position wich activates the pilot-pilot and pilot-ground inter-com. Also, it's compulsory to turn the inter-com off once the engines are not running, to avoid making any unapporopiate comment that might be heard by the ground crew...
Bye.