MaxSez: One requests or receives a Freq Chg on the following occasions;
a) You Request a Freq Chg Upon “Departure” from an aerodrome at a Controlled Field unless a Controlling Agency sends you one prior to arrival at or soon after the field inner circle, (workload permitting) or at first opportunity. Note; Towers Control the airspace of their fields from the Surface to FL-050 within the defining fields inner circle. Competent Tower Controllers who are not inundated or have Departure, Approach or both operational will often make the Freq Chg or a Hand Off automatically. You should Request a Freq Chg after you have past the inner circle boundary at controlled departed field if a Tower does not affect the Freq Chg or Hand off.
b) Alway anticipate Freq Hand Off’s if an ATC structure is operational. Heads up en-route, a Center may be watching you at anytime. If there present Check In and follow the Hand Off instructions up or down the ATC control chain when operational. No Center, expect Approach. No Approach expect Tower, always follow the ATC Chain up and down.
c)Review the comm menu often, once the fires lit, look for newly joined controlling Agencies en-route or in the chocks
d) An Airspace Challenge by ATC like “Your in Controlled Airspace” or “State Intention” Indicates your not following ATC Comm protocol, its poor airmanship. Remember the Pilot in Command is the Decision Maker, but he must be competent!
e)No ATC, Unicom, Pilot initiated all Freq Chgs & chg to a Unicom station to clear an active ATC Flight Strip, Same when out of active contacted airspace always clear the Strip.
That’s my take, correct me if you disagree or would like to add a novel view!