Would you be able to provide a SIP packet capture? A description of the over-all SIP connectivity would help as well.
The TA900's can be programmed to provide call waiting it's self, or can let the switch handle the service.
Switch Controlled flash-hook:
(config)# voice flashhook mode transparent
TA900 controlled flash-hook
(config)# voice flashhook mode interpreted
(config)# voice call-appearance-mode multiple
(config)# voice conferencing-mode local
In our setup, we have opted to use the TA900 controlled flash-hook while providing two SIP trunk's to each voice user.
Should I run "debug voice summary"?
Customer - > TA908 - > SIP trunk over Ciena Gig ERPS Ring - > NV3430 SBC - > Metaswitch
I think you'll want to focus on the NV3430 SBC. I have been able to make call waiting work with a TA908e on the same subnet as our Metaswitch -- DOC-8762 in Metaswitch Communities.
I'm not much familiar with the tools Adtran provides for debugging SIP. I tend to get wireshark / tcpdump captures from the equipment in our path. A switch in between the equipment with port mirroring would do the trick as well.
Some useful commands may be
debug voice verbose
debug sip stack mess
debug sip stack err
debug sip cldu
voice flashhook mode transparent fixed the problem