ringback tone
Definition:
A ringback tone is music that a caller hears when calling your mobile phone. The music replaces the standard ring sound most callers are accustomed to hearing to indicate the call is going through. This is in contrast to a ringtone which is what the person receiving the call hears. Ringback tones can be purchased over the Internet and downloaded to your mobile phone or in some cases, ringback tones can be purchased directly from your mobile phone.