We are trying to install a BT Versatility system at work and everything except incomming and outgoing communication seems to work. When we try to access either line 1 or line 2 on our feature phones we get a busy signal and resieze option, which does nothing.

We have tested the wires to make sure they work and we have plugged in non-PBX phones to make sure that the phone line itself is working. We have tried to cold reboot the machine with and without the batterie attached and we have swithced the line priority to PSTN. We switched pin 2 and 5 on our wire to make sure that that isn't the problem. We removed the ISDN module to make sure that it wasn't interferring with the PSTN as we don't use ISDN.

Otherwise the phones seem to work fine. We can call other extensions in the building with no problem.

Is there anything else we can try to troubleshoot this issue?

You do have a black PSTN module installed in one of the line ports dont you? And have the two lines enabled in sys programming?