ETSI TS 122 038 defines the stage one description of the USIM application Toolkit (USAT). Stage one is an overall service description, primarily from the subscriber's and serving environment's points of view, and does not deal with the details of the human interface itself.

This TS includes information applicable to network operators, serving environments and terminal, switch and database manufacturers.

This TS contains the core requirements for a USIM application Toolkit (USAT) which are sufficient to provide a complete service.

It is highly desirable however, that technical solutions for a USIM application Toolkit (USAT) are sufficiently flexible to allow for possible enhancements. Additional functionalities not documented in this TS may implement requirements which are considered outside the scope of this TS. This additional functionality may be on a network-wide basis, nation-wide basis or particular to a group of users. Such additional functionality shall not compromise conformance to the core requirements of the service.