This TS provides a study, which proves the feasibility of ISDN-based DECT/GSM interworking to support roaming of users of cordless DECT terminals between public GSM networks and private DECT networks via an ISDN-based interface. The study is aiming at teleservice speech and supplementary services. Data, fax and other teleservices are out of scope. In order to limit the amount of work for subsequent specifications to what is achievable within a reasonable timeframe, this feasibility study considers very complex functionality, e.g. inter-network handover, to be out of scope. Commercial viability and demand has to be considered by GSM MoU Association.