G'day Grahame, yes the N is the one I'm talking about. It is on a few different aircraft, but not on all ACARS equipt aircraft like the 767. At the moment I imagine we'll see a few people sending it when not required, and forgetting to send it when it is, but I'm sure that the company will be right onto it!
For the side - Yes you're right that many crew will be fine with it, but conversely a lot don't know that people read their messages. Most crew couldn't care less that somebody listens in or reads what they say, but I'm not so sure they'd be keen to have all of it published on the internet, where those who are not enthusiasts, but the media, and who knows who else can freely read it. If those people really wanted to, yes they could monitor ACARS, but they won't do that, but they might run with something from a web forum (Media frequently quote PpRuNe and other websites as gospel).
Most of the things that you post are completely harmless, and some are rather amusing (I didn't know we had so many comedians flying haha), but personally I'd rather not see messages that are not aviation related, such as personal emails, or emails regarding crewmembers or the public.
Thats my 2c worth anyway
Ash W - Again, and you don't seem to grasp this - my "request" has nothing to do with legality. It is to do with morality. As an aside, unencrypted information is not automatically public domain. And, by the way, don't go listening to telephone calls which you liken to making radio calls. Telephone communications are private, and there are very strong penalties for people intercepting them.