Introduction
Instead of hearing the familiar “ring” tone when calling someone, caller ring back tone (CRBT) lets wireless service subscribers play their favorite tune, sound, jingle, or phrase to incoming callers. With the ability to choose the ring tone a caller will hear, subscribers have an instant way to express their own individuality — and enterprises have the option to provide a customized message to the calling party. The extensive penetration of mobile handsets, particularly among developed countries has increased the demand for a large variety of handset models and related applications. The need for personal expression worldwide has filtered into the cellular phone industry.

An important distinction between color ring back tones and other services is that this network-based solution is independent of both handset and Subscriber Identity Modules (SIM's).

Users are not required to have the newest phone or a specific brand of phone. Therefore, operators have the flexibility to offer personalized ring back services to all types of subscribers (i.e., postpaid or prepaid, fixed or mobile)