You may be running into bug CSCsq67485. The bug states that it is fixed in 6.1.3, but TAC has confirmed that it is not actually fixed until 7.0
CSCsq67485 Bug Details
No ringback tone for SNR calls incoming through the H323 gateway
Symptom:
Callers get no ringtone or one ring and silence
Conditions:
Incoming calls are through H323 gateway; called number is enabled for mobility and call is routed to Remote Destination
Workaround:
In addition to the fix for this defect, please make sure to set the service parameter "Send Progress Timer" to 1 sec more than DelayBeforeRinging Timer
If H323 ICT is used, this "Send progress Timer" should be adjusted to 1 sec more than DelayBeforeRinging Timer in clusters in the call path
This workaround is addressed in CSCsq92647
Thanks,
-Adam
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