Cordless telephone systems are full duplex communication systems that use radio to connect to a portable handset to a dedicated base station, which is connected to a dedicated telephone line with a specific telephone number on the public switched telephone network. In the first generation cordless telephone systems, the portable unit communicates only to the dedicated base unit and only over a distance of few tens of meters. Early cordless telephones operate solely as extension telephones to a transceiver connected to a subscriber line on the PSTN and are primarily for in-home use.
Second generation cordless telephones have recently been introduced which allow subscribers to use their handsets at many outdoor locations within urban centers such as London. Modern cordless telephones are sometimes combined with paging receivers so that a subscriber may first be paged and then respond to the page using the cordless phone. This system provides the user with limited range and mobility, as it is difficult to maintain a call if the user travels outside the area covered by the base station.