A method for revenue assurance in a telephone network. The method comprises receiving a call request from a first user device on a network to a second user device, where the user device associated with a first user account has an account credit value insufficient to complete the requested call. A call timer duration is set to instantly expire on encountering a chargeable event. The call is continued toward the second user device. Upon encountering a chargeable event, the call is released. The chargeable event may be presenting a Ring Back Tone to the caller and confirming that the second device is ringing. The chargeable event may be detecting when the call has been answered.