The Spam Act 2003 is the federal law that governs commercial electronic messages in Australia: marketing sent by email, SMS, MMS or instant message. It is enforced by ACMA, the Australian Communications and Media Authority, which takes complaints and can issue warnings and fines. It applies to every business that sends marketing this way, however small, and it does not matter whether the message is one text to one customer or thousands.
It rests on three requirements. The person must have consented to receive the message. The message must clearly identify the business that sent it and how to contact it. And it must include a functional way to unsubscribe, which must be honoured promptly. The Act also bans using software that harvests addresses from the web, and lists built that way. Phone calls are covered by different rules, including the Do Not Call Register, which applies to telemarketing calls rather than texts; a text still needs consent under the Spam Act.
In practice
A cafe sends one text a month to 300 members. Over a year that is 3,600 commercial messages, and every one of them has to meet all three rules: sent only to someone who agreed, with the cafe's name in it, and with a way out that works.
The rules catch shops out in ordinary ways. A business card in a fishbowl is entered for a free lunch, and its owner is later added to the newsletter. A message goes out signed only with a first name. An unsubscribe request made at the counter is forgotten. None of these is a large crime, and each can still lead to a complaint.
This entry is a plain summary, not legal advice. For anything you are not sure of, check with ACMA, which publishes guidance for businesses.
In Counter Club
Members join only by confirming their own number with a code, every campaign text opens with your shop name, and every message carries the member's own opt-out link. What the message says, and how often you send it, is still up to you. See opt-out and privacy.