Make these additions to the gateway configuration to allow the gateway to generate the ringback instead of the originating switch:
On relevant POTS dial-peers:
progress_ind alert enable 8
progress_ind progress enable 8
progress_ind connect enable 8
Refer to Configuring Progress Indicator in H.323 POTS Dial Peers.
On relevant VoIP dial-peers:
progress_ind setup enable 3
Refer to PSTN Callers not Hearing any Ring Back When They Call IP Phones.
You should be running Cisco IOS? version 12.2(3) or later.
Check that the Cisco CallManager parameter ToSendH225UserInfoMsg is set to True. Go to Service > Service Parameters > Select server > Cisco Call Manager.
For more information on ringback, refer to the No Ringback to PSTN when IP Phones Initiate a Call Transfer (Cisco CallManager 3.0 or Unity Voice Mail) section of Troubleshooting No Ringback Tone on ISDN-VoIP (H.323) Calls.