I know of 1 police agency in the metro Phoenix area that uses plain English for the most part. The fire departments use plain English for the most part as well, although there are a few brevity codes.
When multiple agencies work together on the interop channels, they have to use plain English. i don't think any two agencies here use exactly the same list of brevity codes, and that can cause confusion. I've heard it happen, when an officer from one agency forgets to use plain English, and an officer, or a dispatcher, from another agency has to ask them what they mean, because in the context used, the brevity code didn't make any sense to them.
Either standardize the list (not just the APCO 10-code list, but there's also Code 1 to Code 1000, and some agencies have 11-codes, and I think even 12-codes) and stick to it, or go to plain English.
John
Peoria, AZ