I dont know, just configured BYOC SIP trunk and it worked fine. Then stopped working, it didnt register the SIP account at the registrar. They told some curious info that inbound and outbound gateways have to configured separately as two gateways, one in and one out. I did it, it didnt help. I think it helped after I turned on the SIP ping option in the vapi settings. Ok, the trunks worked fine for a week and yesterday at noon stopped. It is really frustrating and means Vapi will never be a choice for production platform. Just for demos and prototyping