For the first step in this process, we will need to find out the current IP Address being assigned to your Grandstream by your D-Link router. Please refer to How to Receive the IP Address on a Grandstream for information.
Once
you have obtained the IP Address assigned to the Grandstream, now we
need to Disable the SIP ALG, and set that IP to the DMZ in the
DLink.
Open a browser, and navigate to http://192.168.0.1
Once
at the login page, select Admin from the drop down menu, and leave the
password blank (or if you have changed it, type your password in the
box) and click Log In.
Once logged into the DLink, click on Advanced, then click Firewall Settings on the left hand side of the page.
Once at the Firewall Settings screen, scroll all the way down, you will see the DMZ and ALG settings. Check the box labeled Enable DMZ, and type the WAN IP Address of the Grandstream that you obtained in the first step. Also, under the Application Level Gateway Configuration, uncheck the box labeled SIP.
After you have made all the necessary changes, scroll all the way to the top, and click Save Settings.
After
you have made the necessary changes to the DLink, power cycle the
Grandstream, and wait 10-15 minutes before attempting a test call. If you are still unable to dial out, please contact support for additional assistance.