Thank you very much for your reply. I had a couple of questions:
Would this be a possibility sometime in the future?
Would it be possible to allow us, through FreeSBC, to set the interface name to an integer? Because, presently, the contact header is being sent as interface_name (at) ip_address (voip1 (at) 10.0.67.134).
We are keen to get this to work with our SIP trunk provider.
It is not solved but as a workaround, you can change the interface name. For example, if your ISP wants to see 123456789 in contact header user part please change the interface name to 123456789f, sbc will ignore the f and send 123456789 in the contact header