3GPP TS 31.121 V5.2.0 (2005-06) is the technical specification for UICC-terminal interface USIM application test specification (Release 5).
The document is a 3GPP Technical Specification that describes test procedures, default values, and acceptance criteria for the USIM‑terminal interface. It covers a wide range of functional areas such as subscription handling, access control, PIN management, fixed dialing numbers, advice of charge, and PLMN selection.
The specification is intended for use by developers and test engineers working on UICC and USIM implementations. It provides detailed definitions, coding conventions, and step‑by‑step test methods, along with initial conditions and acceptance criteria for each test case.