This Global System for Mobile communications Technical Specification ( GTS) provides a study which proves the feasibility of ISDN-based DECT/ GSM interworking to support roaming of users of cordless DECT terminal s between public GSM networks and private DECT networks via an ISDN-ba sed interface. The study is aiming at teleservice speech and supplemen tary services. Data, fax and other teleservices are out of scope. In o rder to limit the amount of work for subsequent specifications to what is achievable within a reasonable timeframe, this feasibility study c onsiders very complex functionality, e.g. inter-network handover, to b e out of scope. Commercial viability and demand has to be considered b y GSM MoU Association.