An organization that I belong to has an IP-PBX, along with 3 telephones connected to it. They have 2 phone numbers going to the PBX. When the PBX was first installed, it was working okay for a few months. But after a while, callers that would call the organization would get a busy signal. Sometimes just 1 of the 2 phone numbers would have a busy signal, but most of the time, both phone numbers would be busy. But callers inside the organization are always able to dial out, whether the callers calling the organization get a busy signal, or not. We tried to fix this problem by unplugging the power cord from the PBX for about 10 seconds. When we plugged it back in, callers would not get a busy signal anymore. But after a few days, callers start getting a busy signal again, and the PBX has to be unplugged, and plugged back in again. This happens just about every week. So in other words, callers inside the organization are always able to dial out, but callers calling the organization usually get a busy signal, even when none of the telephones are off the hook. I am not sure about the PBX’s brand or model number. Can anyone please give me any ideas on what can be done to correct the problem that my organization is having? Could it be a cabling issue?