Below are my debugs, I'm not able to tell if there is something wrong with the setup. I've tried both ringback override options neither work.
23:09:13.374 SIP.STACK MSG SIP/2.0 180 Ringing
23:09:13.374 SIP.STACK MSG Via: SIP/2.0/UDP 10.40.1.3:5060;branch=z9hG4bK-386b89-dc64123d-430212c1;received=10.40.1.3
23:09:13.375 SIP.STACK MSG From: "REYNOLDS REYN" <sip:9795952600@10.40.1.2:5060;transport=UDP>;tag=4ad7528-a280103-13c4-386b89-2667b110-386b89
23:09:13.375 SIP.STACK MSG To: <sip:5140@10.40.1.2:5060>;tag=as64a72c6c
23:09:13.375 SIP.STACK MSG Call-ID: 4b2b550-a280103-13c4-386b89-302ac3fb-386b89@10.40.1.2
23:09:13.375 SIP.STACK MSG CSeq: 1 INVITE
23:09:13.375 SIP.STACK MSG User-Agent: RRPBX
23:09:13.376 SIP.STACK MSG Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO
23:09:13.376 SIP.STACK MSG Supported: replaces
23:09:13.376 SIP.STACK MSG Contact: <sip:5140@10.40.1.2>
23:09:13.376 SIP.STACK MSG Content-Length: 0
23:09:13.376 SIP.STACK MSG
23:09:13.379 TM.T01 71 Delivering rcvd SIP call-leg response: 180 Ringing
23:09:13.379 TM.T01 71 Delivering No body in message when trying to get SDP
23:09:13.380 TM.T01 71 Delivering rcvd: Provisional Response 180 Ringing (no SDP)
23:09:13.380 TM.T01 71 Delivering State change >> Delivering->SipTM_Ringing
23:09:13.380 TM.T01 71 SipTM_Ringing sent: TA->Alert
23:09:13.381 TA.T01 71 TAOutGoing rcvd: alert from TM
23:09:13.381 SB.CALL 105811 Delivering Called the deliverResponse routine from Delivering
23:09:13.381 SB.CALL 105811 Delivering Alert sent from T01 to T02
23:09:13.381 SB.CALL 105811 State change >> Delivering->Alerting
23:09:13.381 TA.T02 43 TAConnectWaitIn alert event accepted
23:09:13.381 TM.T02 43 IsdnTmStateInboundAccept->IsdnTmStateInboundAlerting
23:09:13.382 TM.T02 43 IsdnTmStateInboundAlerting::enter()
23:09:13.382 TONESERVICES.EVENTS t1 0/3.8 - empty - Ringback Generation: Request resource
23:09:13.383 TONESERVICES.EVENTS t1 0/3.8 - Dsp 0/1.3 - Ringback Generation: DSP channel allocated for the resource
23:09:13.383 TONESERVICES.EVENTS t1 0/3.8 - Dsp 0/1.3 - Ringback Generation: constructed
23:09:13.383 TONESERVICES.EVENTS t1 0/3.8 - Dsp 0/1.3 - Ringback Generation: starting
23:09:13.384 TONESERVICES.EVENTS t1 0/3.8 - Dsp 0/1.3 - Ringback Generation: TDM map
23:09:14.222 SIP.STACK MSG Rx: UDP src=10.40.1.2:5060 dst=10.40.1.3:5060
Are you running older firmware? There's a bug fixed in R11.10.6 that addresses this issue. AOS R11.10.6 Release Notes
It was previously on R11.4.1 I've changed it to 11.4.6 which we use at all of our other locations without this problem and I am still having the same issue.
This sure looks like that bug, I'd upgrade to a currently supported firmware.