Gentlemen,
Please correct me if I am wrong, but don't the rules of CTA allow the pilot to make a deviation from the clearance for the safe conduct of the flight and inform ATC afterwards? If that is the deal, then if you couldn't get on the frequency due congestion, the prudent path would be to do what you needed to remain in VMC and then tell ATC ASAP when you could get the call in.
Walrus