Well once when I was on bike patrol the radio system was being crappy (not digital yet and every so often it gets hard to hear), so I just called the non-emergency number to talk to them. The call taker was the same woman that was dispatching and they only have like 3-4 people on shift who are all dispatchers.

But in the most usual case, just use plainspeak. Unless you are a part of that department and you know their specific codes, just talk like a normal person. As an explorer, I know that my department doesn't use the average codes.