Router Info Sonicwall
Disable SIP Header Transformations and Enable Consistent NAT
Create Outbound NAT Policy and Disable Source Port Remap
In some cases the SonicWALL will remap the 5060 and 10000-20000 UDP source ports causing one way audio and calls dropping after 30 seconds.
To resolve this, create an inside to outside rule like the following:
PBX Private IP
After that go to the Advanced tab and check the box for "Disable Source Port Remap" and click OK.
Once completed the PBX will always use the proper source ports on the WAN side.
Create Access Policy with Increased UDP Timeout
Most often seen in cloud deployments you will see phones going REACHABLE/UNREACHABLE with complaints of calls going directly to voicemail and BLFs not lighting properly.
To fix this add a LAN to WAN Access Policy as follows:
Navigate to the Advance tab and reduce the UDP timeout to 30 seconds, once saved phones should remain REACHABLE.