An address is the telephone number, complete with national or international codes, of a telephone, fax machine, or other device that can receive calls. Addresses can be dialed by a human or stored in an electronic directory for retrieval and use (dialing) by a telephony application.
A line can have a local address. The user or an application sets this address when installing the service provider that supports the line. The service provider controls the local addresses of a line. In the simplest case, each line has one address. However, any line can have more than one address.
The service provider has a configuration. The service provider gives users access to the configuration settings by providing a TSPI_lineConfigDialog function.
In POTS, multiple addresses work only with systems that support distinctive ringing or are connected to a DID (direct inward dialing) trunk. DID is an extra-fee service provided by the phone company. With DID in a multiuser voice mail system, the dialed number is signaled to the system on the DID trunk before the call rings. This allows the system to play the called party's pre-stored announcement message and to store any incoming messages in the correct voice mailbox.
On a residential line with distinctive ringing service, different ringing patterns correspond to multiple numbers assigned to the same line.
ISDN allows simultaneous multiple addresses by providing multiple channels, each having a unique address.