I have a Netgear FVG318v1 and my calls dropout at 20 seconds, why does this happen?

Overview
Step 1: Login to the Netgear FVG318v1
Step 2: Disable SIP ALG

Note: The FVG318v1 suffers from a SIP ALG problem. The latest firmware update needs to be applied and SIP ALG needs to be disabled to stop the call dropouts. Version 1 can also be updated to version 2.
See this links for further details.

http://kbserver.netgear.com/products/FVG318v1.asp
http://kbserver.netgear.com/products/FVG318v2.asp

Step 1: Login to your Netgear FVG318v1
  1. Open up your web browser.
  2. Log in to the router at its default LAN address of http://192.168.0.1
  3. Login with username of admin, default password of password.
Step 2: Disable SIP ALG
  1. Go to Rules
  2. Scroll down to the bottom of the page and you will see various options such as SIP ALG
  3. Make sure it is ticked.
  4. Dropout issue has been solved