I'm looking for guidance on radio communications when taking off from Delta airspace and flying into Charlie that starts where the Delta ends. My aircraft can only monitor one frequency at a time. Can I just tell the Delta tower I'm flying into Charlie and request a frequency change while still in Delta in order to establish comms with Charlie tower before entering Charlie airspace? If so what would be the preferred phraseology?
Typically, the class D tower will tell you you to when to change frequencies and it will most likely be to the class C's approach control, not their tower. You will hear something like, "Nxxxx, contact Class C approach on 123.45" and you can respond and change frequencies at that point. You still have to follow the rules for entering class C airspace.