sentences:  Hybrid DECT/GSM devices have appeared, but these have essentially been "Two phones in a box" systems that combine the functionality of a standard GAP phone with a GSM phone, so that a person can receive and make calls on either their home phone line or a mobile network without having to use two phones.An example of this approach is BT's/Ericsson's OnePhone service.Most probably, the fact that the system requires an ISDN connection, which in most countries where ISDN is popular is priced by time used, has made GIP a difficult sell.