At my office we have a new phone system called Microsoft Response Point. The system we have was made by D-Link. Great system, you can read countless good reviews on it. However we had a problem with external calls. If the inside caller and the external caller tried to talk at the same time the inside caller would not be able to hear the external user.
The way I finally managed to get this fixed, is by logging into the Response Point Gateway – DVG-3104MS – Remember its IP:9999. The username by default is admin along with the password of admin. Click Advanced and then click Call Control on the left. Change the Default Codec to G. 726-32.
I’m not saying that’s the only way to fix the problem, but that seemed to work for us. You can play with the different codec options and see which works best.