OPT - OUT

An opt-out is special feature (required in many countries) added to promotional messages, that allows handset users to unsubscribe from receiving any further SMS from the sender.
Typically, there are several forms of opt-out used in SMS industry :

1. MO SMS – in this case, the handset user may send a message as a reply to the number the original MT SMS was received from, saying something like “STOP”, “NO”, “UNSUBSCRIBE” etc. This type of opt-out is commonly used in China (TD, N, 0), Russia and many other countries.
2. Auto-response system – this option is used in South Korea. The government implemented a system where any company willing to send promotional messages must include an opt-out via Toll Free number beginning with 080-… The main point here, is that is the handset user is willing to unsubscribe from receiving any SMS in the future, the process of opting-out must be free for them. The companies renting 080 numbers are the ones paying for the service, so everyone (more or less) is happy.
3. Link in the body of the message  – “to opt-out from receiving any more news from http://www.ournews.com please go to your personal page and choose the unsubscribe box” – this one is relatively popular as well. A lot of companies, especially e-commerce or online magazines / newsletters are bound to use this option simply because people who subscribe to the services are from different countries and following opt-out regulations for each and every one of them is extremely hard. But, in this case the chance of handset users raising a claim with their mobile carrier and the line getting blocked is very high as well.

In the end, the best way to make sure no laws are broken and the local government is not suing your company for harassing the citizens is to be a step ahead and get all information possible before entering any market with your SMS campaigns.