For what its worth these are VTEC's "rules":
"If youre in the quiet coach, the idea is to keep the noise down. Mobile calls and noise from electronic devices are strictly forbidden (now is not the time to review your ringtone collection), and conversations should be conducted quietly. If you do have to make or take a call, please move into the vestibules before dialing or answering."
Why is the above so difficult to grasp for some people?
A phone is a device that incites IMMEDIATE attention, it is hard to ignore a ringing phone when you are in a position to answer it, so people do this without thought. It will also depend on whether they are expecting an important (to them) call.