SIM Application Toolkit
SIM Application Toolkit (commonly referred to as STK) is a standard of the GSM system which enables the Subscriber Identity Module (SIM) to initiate actions which can be used for various value-added services.
The SIM Application Toolkit consists of a set of commands programmed into the SIM which define how the SIM should interact directly with the outside world and initiates commands independently of the handset and the network. This enables the SIM to build up an interactive exchange between a network application and the end user and access, or control access to, the network. The SIM also gives commands to the handset such as displaying menus and/or asking for user input.
STK has been deployed by many mobile operators around the world for many applications, often where a menu-based approach is required, such as Mobile Banking and content browsing. Designed as a single application environment, the STK can be started during the initial power up of the SIM card  and is especially suited to low level applications with simple user interfaces.
In GSM 2G networks, the SIM Application Toolkit is defined by the GSM 11.14 standard released in 1995. From release 4 onwards, GSM 11.14 was replaced by 3GPP 31.111 which also includes the specifications of the USIM Application Toolkit (USAT) for 3G networks.
- Some manufacturers claim that STK enables higher levels of security through identity verification and encryption, which are necessary for secure electronic commerce.
- STK has been deployed on the largest number of mobile devices.
||This article uses abbreviations that may be confusing or ambiguous. (September 2010)|
- Updating STK applications and menus stored on the SIM can be difficult after the customer takes delivery of the SIM. To deliver updates, either the SIM must be returned and exchanged for a new one (which can be costly and inconvenient) or the application updates must delivered over-the-air (OTA) using specialized, optional SIM features. Mobile Network Operators can now (as of October 2010[update]), for example, deliver updated STK application menus by sending a secure SMS to handsets that include a SIMalliance Toolbox (S@T) compliant wireless internet browser (WIB). When using a Bearer Independent Protocol-compliant (BIP) SIM card in a BIP-compliant handset, the updates can be delivered very quickly as well (depending upon the network connectivity available to and supported by the handset, i.e. GPRS/3G speed). It might also be possible to change the menu of wireless internet gateway (WIG)-based STK applications. The update limitations hinder the number and frequency of STK application deployments.
- STK has essentially no support for multimedia, only basic pictures.
- The STK technology has limited independent development support available.
STK and CAT in 3G 
Card Application Toolkit (CAT) is now used as the more generic method used describing the UICC's more extensive STK features.
- SIM Toolkit
- SIM Toolkit
- SIM Toolkit
- Gemplus to Deliver SIM Card-Based Solution to Oi For First GSM Launch in Brazil - Smart Card Alliance
- ETSI TS 102 223 V9.1.0