Color Ring Back Tone (CRBT) is one of the most successful enhanced Value Added Services for wireless (Mobile Telephones), and now also available for wireline (Fixed Telephones) service providers. It is a service by which the person who is receiving the call can customize the ring back tone, based on the phone number of the person who is placing the call. CRBT is self-propagating, spreads virally by using readily available contents like songs, Music, Speech etc.. Revenue generated through this service can easily grow from 0 to Lakhs and Crores in a few years. Since it is completely controlled and delivered by network-based signalling servers, CRBT has the advantage of allowing complete operator control with minimal customer and handset interaction.

To use CRBT, a customer (usually wireless) selects a specific song or audio file to play instead of the standard ring tone heard while a call is connecting. Revenue is generated through monthly CRBT subscription charges and a CRBT download fee whenever the customer selects a new song or audio file.