What is the use of SIM card application on mobile phone?

Stk(sim Toolkit) allows sim based on smart card to run its own application software.

Stk card can receive and send gsm short message data as an interface between sim card and short message, and it also allows sim card to run its own application software. These functions are often displayed on the mobile phone screen that can be activated by software, and the mechanical "dial-listen-answer" mode is replaced by a friendly text menu, so that users can easily carry out complex information retrieval operations or transactions by pressing keys.

Stk provides a developable environment for the value-added service of sim card, that is, a simple and easy-to-operate development platform. The content of the menu item is read by the mobile phone from the stk card and cannot be modified by the user. Depending on the stk type, the content of the menu item may not be fixed and can be changed through the air interface.

This menu will only be displayed if your sim card supports it. The name and content of the menu depend on the available services.