We have this odd issue where only a few outgoing calls either ring constantly or immediately ring busy. Nothing changes as far as I can see on the configuration or the invite or anything. I can't see any correlation for the phone numbers, at first it seemed that it was cellular phones on T-Mobile. I'm not sure what to check to see why this happens. Unfortunately, my provider isn't one of the ones listed on the supported providers for 3CX, so I had to manually put in the settings. If anyone has any suggestions what it could be, I can work with my SIP provider to see what we can do. Thanks!