Bill Denton wrote:

Would it be improper to ask for a frequency change or to advise that you
are leaving the frequency, or just not necessary?

You only *need* to ask for this if you want to switch while in their
airspace. I've hit this case occasionally, and I cannot recall it being a
problem.

For a class D w/o real RADAR (ie. CDW or MMU in my neighborhood), I'll call
when clear just to let them know. For better equiped class Ds, ie. TEB or
RDG, they get rid of me one way ("contact departure") or another ("squawk
VFR").

- Andrew