I did read a thread here in the last few days, stating that they've
started to send EDR offers by SMS.
As to opting-out/in, you should be able to do this
via the EDR website (login required), or by calling the EDR Customer Service Centre 1300 10 1234, or as noted by
LiamR below - a reply SMS with the word STOP to 0428239277.
On the question of spam, it actually doesn't meet the definition of spam as covered in the
Spam Act 2003 (Cwlth). Because you have an existing business relationship with the entity (in this case EDR) AND have provided them your mobile number, they are well within their rights to contact you via any means UNLESS you have explicitly opted out.
An offence under the act is only created IF they have sent you an unauthorised message AFTER you have explicitly opted out of receiving such communication.
I won't talk about the fact the Spam Act enshrined opt-out, as it's still a big bone of contention for me.
And while not directly related to the OP, the offence relating to the use of voice communications for marketing purposes is within the legislation that enabled the Do Not Call registry (and surprisingly for me, this is one piece of legislation that I don't know the name of the act or citation for this one off the top of my head).