Does SMS belong to online or offline?

Hello, mobile phone short message advertising (commonly known as short message mass sending) is to send short messages to mobile phone users to convey information such as products and services of enterprises, so as to achieve the purpose of advertising. It belongs to a kind of online advertising, that is, online advertising. However, SMS advertising is controversial because of its legitimacy and rationality, and its prospect is very embarrassing. Nowadays, mobile phone applications, game advertisements and wap advertisements are very popular. The form is much more diverse than SMS, and you pay according to the click effect. Google and Apple, the two largest Internet companies in the world, have acquired the reorganized admob and iAD respectively, and the leading domestic mobile phone advertisements are of this type. The prospect is good, so the competition is fierce.