The scope of the present document is to describe 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 or a radio network such as GSM. Due to the time constraints to have a first specification ready for market needs@ a phased approach is necessary. The first phase aims primarily at an application supporting the speech teleservice (including DTMF support) in a residential single cell environment. The focus is on the requirements necessary to elaborate the radio interface and the security aspects for such an application. To not prevent or impede the evolution of CTS to additional services and functions@ later phases may have to be considered when now defining the means to fulfil the above mentioned requirements for the first phase of CTS. Therefore@ additional support on the CTS radio interface for later phase services (e.g. SMS@ subscriber authentication and GSM supplementary services)@ is included already in CTS Phase 1@ provided that such services are clearly defined. Other expected services and functions in later phases are included in annex A. The standardisation of the physical layers of the GSM-CTS fixed network interface is not in the scope of the present document. However@ consideration may need to be given to communication of application data between CTS and PLMN via the fixed network.