It is imperative to include an opt-out/unsubscribe function in any broadcast SMS message, especially if it's promotional in nature.
A popular option is to include the phrase "Reply STOP to OptOut" allowing the mobile to reply via text.
Alternatively, you can use the [[STOP]] command to insert a clickable link, for example "Click [[STOP]] to OptOut".
When sending to a blacklisted mobile number, the SMS will fail with the result "Destination is blacklisted" and you will not be charged.
TNZ's SMS service includes an automated unsubscribe tool.
When a SMS is received that begins with 'stop', 'optout' or 'unsubscribe', the mobile number will automatically be added to your Dashboard Blacklist.
You can view the list of opt-outs at Dashboard Blacklist.
Using the Dashboard Blacklist tool, you can manually add opt-outs.
You can also add a mobile number to the list under View Messages | SMS Received, checking the box next to the received message, and clicking Add to Blacklist.