A telephone subscriber may have one or more installations at his or her place of subscription. Each subscriber is identified by a unique subscriber number. The name and address of the subscriber is also recorded as well as the number of installations. The date of the last payment should be recorded against each subscriber.
Asscociated with each installation there is usually at least one, and possibly several handsets supplied by the telephone company. A handset is identified by a unique serial number. Other attributes are colour and type. An increasing number of handsets are now provided by subscribers themselves. In this case the details are not recorded.