Short message service (SMS) that has been widely used in various fields could potentially utilized for problem-solving consulting services that are based on expert system, so it takes a kind of application platform to implement this service. This paper proposes an expansion of online expert system services (web and wap based) by adding an application use SMS interface. Knowledge base of the expert system, which employs a decision tree approach, is expressed in the form of a database that can be accessed by the application interfaces, including SMS interface. According to the experiment results, the decision tree has been able to play a role directing the consultation mechanism from an initial question to reach a conclusion interactively. Thus, a problem-solving case that can be expressed in the decision tree allows the implementation of this system.