This object specifies the storage type for this
conceptual row. If this conceptual row represents
a programmable tone in a system built-in tone plan,
the value of this object is permanent (4).
If this conceptual row represents a programmable tone
in an user defined tone plan, the value of this object
is nonVolatile (3).
If the value of this object is permanent (4),
cvtcProgrammableToneDuration is the only object can be
modified by the user.