I'm not sure how much I can offer on this without breaking the rules of this board. Are you able to get support from a Toshiba vendor?
If your domain name and/or sip server are an internal IP, likely the adtran, you can switch the next hop back to the firewall. If the domain name and/or sip server or a public address or a fqdn name that won't work. Understanding how IP traffic works here is necessary.
