A ringtone or ring tone is the sound made by a telephone to indicate an incoming call. The term, however, is most often used to refer to the customizable sounds available on mobile phones.

A phone only rings when a special "ringing signal" is sent to it. For landline telephones, the ringing signal is a 90-volt, 20-hertz, AC wave generated by the switch to which the telephone is connected. For mobile phones, the ringing signal is a specific radio-frequency signal.

A telephone ring is the sound generated when an incoming telephone call is received. The term originated from the fact that telephones notified the user to an incoming call by repeatedly striking a bell or bells, producing a ringing sound. This "Magneto" bell system is still in widespread use. The ringing signal sent to a customer's telephone utilized AC at 90 volts and 20 hertz in North America. While the sound produced is still called a "ring," more recently manufactured telephones electronically produce a warbling or chirping sound. The signal is sent for every ring and allows phone operators to provide several services with different kinds of rings (for example, rings with a shorter interval between them might be used to signal a call from a given number). When a phone rings — either landline or mobile/cell phone — it may carry Caller ID information and present it on a screen.