These settings will allow SIP traffic to work properly through SonicWALL firewalls.
Change Firewall and VoIP Settings
Firewall => Advanced => Scroll down to "UDP":
Increase UDP timeout to 120
VOIP => Settings:
o Turn on Consistent NAT.
o The SIP Transformations sections should be DISABLED (unchecked).
Add Firewall Rule
Firewall => Access Rules:
Add an 'Access Rule' for any traffic from WAN Network 126.96.36.199 Netmask 255.255.255.224 to the LAN. (shown)
Also, add an 'Access Rule' for any traffic from WAN Network 188.8.131.52 Netmask 255.255.255.240 to the LAN. (not shown)