Mobile applications are getting more and more part of our daily life. Whereas applications running on a mobile phone are common today, the SIM Card is not yet intensively used as an application platform. With mobile con-tactless applications and emulating smartcards as well as mobile TV using sophisticated encryption and authenti-cation, the SIM card is now getting more an more popular for application developers. Topical sales figures clar-ify the enormous business potential of SIM Cards as application platforms.
In the current paper we present our implementation of a Socket Server running on a SIM Card using the Bear Independent Protocol (BIP) as well as application scenarios on top. We give a general overview of SIM technol-ogy as well as a comprehensive introduction for using the SIM Card as an application platform with all pros and cons. The main part describes and discusses the architecture and implementation of a Server on the SIM and lines out potential use cases. 
Although the SmartCard Webserver (SCWS) is recently standardized in OMA, ETSI and JavaCard Forum, we provide a light-weight implementation running on any BIP enabled SIM Card. Besides serving applications with SIM features, the Socket-Server also can be accessed remotely and supports HTTP, too.
Furthermore the server also can be switched into proxy mode. Thus for example any application running on the handset (e.g. J2ME) could use the proxy as gateway. Hence the SIM card would take care of the connection handling as well as the authentication and encryption. This results in a secure end-to-end encryption between the handset and the application server. In such a case the applications on top don’t have to deal with encryption or authentication as the SIM Card hold keys and credentials and takes over this part during the communication. 
The proposed implementation is used in the context of a combined access-control and home automation system where the mobile phone is in control of the appliances in a building. The implemented server is based on a JavaCard enabled SIM and uses the BIP-Server/Client mode and IP for communication with clients. Moreover the implementation of HTTP enhances the number of Web-based use cases.