It is a law requirement to get consent from customers before you send them SMS messages. Whether it is express or inferred, getting consent is a mandatory requirement for any business or organisation before sending out commercial SMS messages. Opting in is one form of express consent. Examples of this could be filling in a form on the company website, ticking a box on a website, talking over the phone, meeting face to face and swapping business cards etc. This gives your business the right to send out SMS messages.
Inferred consent, on the other hand, is not that straightforward. Inferred consent can occur via existing business or other business relationships. So for example if you are a financial institution or retail, your existing customers have reasonable reasonable expectation to receive SMS or emails from these organisations telling you about their products and services. However, some organisations such government bodies, registered political parties, NGOs and educational institutions are exempt from the Spam Act, so the above consent requirement does not apply to them.
Given the need for businesses to reach customers through SMS marketing, any business relying on SMS outreach should note that even with consent, it is good business practice to send customers and stakeholders relevant content, to exercise restraint by not bombarding them with messages and to have clear call to actions in their messages. That way, business can send SMS Messages ethically to avoid potential law suits.