Click “Start” then “Run” and enter cmd and push the enter key
In the command window enter “telnet 10.0.0.138″ (NB: Change 10.0.0.138 to your internal router IP), If you get a command unknown then you will need to activate the Telnet client, Click here to view the instructions
In the username field enter Administrator and push enter, for the password box push enter
Type connection unbind application=SIP port=5060 and push Enter
Type saveall and push Enter
Type exit and push Enter
Now reboot your VoIP phones and they should register with SIP ALG interfering with the registration.
Mac users
Click the Finder icon, then select Applications, then Utilities and double click Terminal
In the command window enter “telnet 10.0.0.138″ (NB: Change 10.0.0.138 to your internal router IP)
In the username field enter Administrator and push enter, for the password box push enter
Type connection unbind application=SIP port=5060 and push Enter
Type saveall and push Enter
Type exit and push Enter
Now reboot your VoIP phones and they should register with SIP ALG interfering with the registration.