The scope of this document is to provide the basis for a description of the Service aspects of a GSM Cordless Telephony System (CTS), which provides the possibility for users of GSM terminals to have cordless access to a fixed network, such as PSTN/ISDN. Due to the time constraints to have a first specification ready for market needs, a phased approach is necessary. The first phase focuses on the requirements necessary to elaborate the radio interface and the security aspects for an application supporting the speech tele-service (including DTMF support) in a residential single cell environment. As a consequence, a full business environment with all services is not considered. In particular, hand-over between CTS fixed parts or between CTS and GSM PLMN is not considered. The standardisation of the CTS interface towards the fixed network is not a scope of this document. However, consideration may need to be given to communication of application data between CTS and PLMN via the fixed network.