available on most cellular telephones
which permits one to change the ringer
on their device
Cellular telephone users usually change their ringing tones to differentiate themselves from others, so that they actually know when it is their phone which is ringing.
Later technology allowed for users to program different ringing sets for different inbound calls. Thus it was possible to have an 'important sounding' ring for one's work, and a subtle ring (or none at all), for one's mother-in-law.