VoIP and Sonicwall:

UDP Timeout, Firewall Settings, Flood Protection, Default UDP Connection Timeout, Set-180
Also do this at Firewall, Access Rules, Matrix LAN-WAN, LAN-VPN, VPN-LAN
Consistent NAT, VoIP, Settings, Check Enable consistent NAT,

Disable SIP ALG on SonicWall Devices
    Log into the device's web configuration utility.
    Select VoIP, Settings.
    Check Enable consistent NAT.
    Uncheck all other Settings.
    Click Accept.

http://help.sonicwall.com/help/sw/eng/6200/25/6/4/VoIP_voIPOptions.html
Using the Public Server Wizard

The SonicWALL Public Server Wizard provides an easy method for configuring firewall access rules for a SIP Proxy or H.323 Gatekeeper running on your network behind the firewall. Using this wizard performs all the configuration settings you need for VoIP clients to access your VoIP servers.
Step 1
Click Wizards on the SonicOS navigation bar.
Step 2
Select Public Server Wizard and click Next .
Step 3
Select Other from the Server Type list.
Select SIP from the Services menu if you are configuring network access for a SIP proxy server from the WAN.
Select Gatekeeper RAS if you are configuring network access for a H.323 Gatekeeper from the WAN.
Select H.323 Call Signaling for enabling Point-to-Point VoIP calls from the WAN to the LAN.
Step 4
Click Next .
Note
SonicWALL recommends NOT selecting VoIP from the Services menu. Selecting this option opens up more TCP/UDP ports than is required, potentially opening up unnecessary security vulnerabilities.
Step 5
Enter the name of the server in the Server Name field.
Step 6
Enter the private IP address of the server. Specify an IP address in the range of addresses assigned to the zone where the server is located. The Public Server Wizard will automatically assign the server to the zone in which its IP address belongs. You can enter optional descriptive text in the Server Comment field.
Step 7
Click Next .
Step 8
Enter the public IP address of the server. The default is the WAN public IP address. If you enter a different IP, the Public Server Wizard will create an address object for that IP address and bind the address object to the WAN zone.
Step 9
Click Next .
Step 10
The Summary page displays a summary of all the configuration you have performed in the wizard. It should show:
Server Address Objects - The wizard creates the address object for the new server. Because the IP address of the server added in the example is in the IP address range assigned to the LAN zone, the wizard binds the address object to the LAN zone.
Server Service Group Object - The wizard creates a service group object for the services used by the new server.
Server NAT Policies - The wizard creates a NAT policy to translate the destination addresses of all incoming packets with one of the services in the new service group and addressed to the WAN address to the address of the new server. The wizard also creates a Loopback NAT policy
Server Access Rules - The wizard creates an access policy allowing all traffic to the WAN Primary IP for the new service.
Step 11
Click Accept in the Public Server Configuration Summary page to complete the wizard and apply the configuration to your SonicWALL.
Tip
The new IP address used to access the new server, both internally and externally, is displayed in the URL field of the Congratulations window.
Step 12
Click Close to close the wizard.