What will the caller hear if Cisco Unified ICM sends back a label of 91919191?

 If Cisco Unified ICM sends back a label of 91919191, the caller will hear ringing. This is because 91919191 is a special label that is used by Cisco Unified Customer Voice Portal (CVP) to play a ringtone to the caller while the call is being transferred to an agent or another destination1. The ringtone is a WAV file that is stored on the media server and is configured on the CVP Operations Console and the VXML gateway1. The label 91919191 is matched by a dial-peer on the VXML gateway that invokes a ringtone service and sends the ringback.wav file to the ingress voice gateway2. The caller will hear the ringtone until the call is connected or disconnected1.

References: Configuration Guide for Cisco Unified Customer Voice Portal, Release 11.6(1) - Unified ICM Configuration [Cisco Unified Customer Voice Portal] - Cisco1, Distributed Voice and VXML Gateway Design with CVP SIP - Cisco Community2