The first action code used on a mobile phone was via SMS text. Usually, it takes the form of sending a word or phrase to a particular phone number or short code. Once this message is received, a return message is sent to the originating phone with the desired content.
The main benefit of using SMS text as an action code is that it is available on 100% of all mobile phones in use since 2008. It does not require a camera or an app to use. And, the process of sending an SMS message is widely understood by likely users of action codes.
Generally, SMS text is used in conjunction with other methods. It would be common for a publisher or advertiser to use a 2D barcode and then augment it with an alternative by saying “OR TEXT ‘MESSAGE’ TO xxxxx.” This method provides a seamless experience for 2D barcode users, with a back-up of SMS text for others.
Many Nellymoser campaigns include SMS text as an alternate activation code.