There is this article. The message I reproduced in my OP seems a bit like Point #1 in that article. Also, last month, my wife received a series of SMS messages which seemed a bit like the "Text Message Scam" described further down the page. Fortunately, it turned out to be a genuine case of a wrong number. (The text messages were charged at normal rates by our mobile carrier, so they weren't going to some expensive premium service).
The 'STOP' code mentioned here is also mentioned in the ACMA article linked above. One thing worries me, however: if sending the 'STOP' code is the same "opting out" of spam, could it have the same effect, i.e., spam increases? After all, clicking on an opt-out link in a spam merely confirms to a spammer that one's email address is valid. The Short Message Service usually (in my experience) neither confirms nor denies that the number to which a message has been sent was a valid one; neither is there any confirmation of receipt of the message. Maybe sending the 'STOP' code will result in more SMS spam, just as it does with email, and, from a variety of message service providers, again just as email spammers do now. Anyway, there's no "SpamCop for Mobiles" yet, so, AFAICS, there's no easy and foolproof way to report these things.
Looking at the message I posted, the message centre seems to be in the UK. I suppose this means that if I send a 'STOP' code, it will be an international SMS (note also that the number starts with '19').
I might have a poke around the communications newsgroups (especially any dealing with mobile comms) to see what I can find. I seem to remember reading an article in the Sydney Morning Herald a couple of years ago, which described how mobile phones in Europe were being hijacked by scammers in some way, with large bills being charged to unsuspecting users. It was too long ago, and I can't remember the details now. My mobile is (fortunately) not internet-capable. (I have also read that a small number of mobile phone viruses are already in circulation).
Anyway, thanks once again for the links. I'll continue my research and if I can find any further info, I'll post it here.