those sja code lists are mainly for the medical reports for the purpose of compiling medical stats. You dont hear them being used much on air... we'd mainly use the transmission codes... if we could remember them!
when i was an ambo and the data went down and we had to rely on the voice it was quite hectic at times, but we all knew to keep the talk to a minimum and often we would use mobile phones to communicate on emergencies too to 6ds.
when i was an ambo a few years ago they trialed a new 'yelp' siren that cut in over the nomal 'weewhaa' and it failed dismally. The activation button is on the floor for the left foot. dont know what they have now.