There is an updated version of the router firmware which fixes the issue. The update can be found at:
http://www02.bezeq.co.il/support/Pages/toalhuti.aspx
Save the first file in c:/
Point your web browser to 10.0.0.138
User name: Admin
Password: Admin
Unplug the phone cable from the router
Go to management from the menu on the left
Click on update Software (or Firmware)
Browse to choose the file that you saved in the c:\ drive
Hit the update button
Then, unplug your VoIP box, wait 30 seconds, and then plug it back in. Wait 15 minutes to ensure the VoIP has settled, and then replug in your phone cable to the router again.