DNR, often called a scratch, in track, refers to instances where an individual withdraws from the race before it begins. Not the same as DQ (or disqualification), in which a runner is removed after the start. Occasionally, in hand-timed races where there are less timers than runners, DNR will be used to indicate that a runner did not finish fast enough to have his/her time recorded.
This is probably one reason why gangsters uses burners or throwaway phones. Another is that law enforcement entities can remotely listen in and record conversations through remotely activated speaker/mic systems in the target's celly -- even with the phone turned off.