Traditional cordless telephones come with a base station that you need to connect to the telephone socket. This base station is already integrated into the Internet-Box; now you only need the handset with a charger. DECT is a transmission standard for wireless telephony at home. (DECT = Digital Enhanced Cordless Telecommunications)
Another advantage of a base station is that all devices can access the same main address book.
DECT handsets have a range of up to 100 m outdoors. In a typical house with walls, room dividers etc. the range is approx. 50 m, although various factors can influence the range.