I will try to make a call pluging a good working phone on the PBX port of the A800.
If the volume is good from that port, but bad when you try to go phone -PSTN-A800, the trouble is the loss betwen the location where the A800 is located and the phone company building.
In same countries, they use very samll gauge wires, and you could have up to close to five miles of wire betwen you and the nearest phone company equipment.
And even on very urban areas you could find this trouble. People complainign of low volume on the middle of big cities.