For example, if two or three people, as roommates, share a residence, each can have his/her own telephone number, and a phone set in his/her own bedroom, equipped with a "ring selector" that is set to filter out all but one particular ringing pattern.
In Ontario, the feature is commonly referred to as Ident-a-Call (Bell Canada), in western Canada Smart Ring (Telus and Northwestel), as well as Teen Ring.
In the United States, AT&T refers to the feature as RingMaster, in Australia Telstra refers to the feature as Duet and in the UK, it's known as Call Sign by British Telecom.
The feature can be used, in conjunction with ring-recognition software or hardware, to allow voice and fax to share a single phone line, though with only one call at a time.
It is also often promoted as a means of incoming call recognition when the line often rings for other members of the household.