The number of Analog trunks (i.e. FXO ports) is determined by the number of O2 modules (one O2 module contains two FXO ports, i.e. 2 analog trunks) and SO modules (one SO module contains one FXO port, i.e. 1 analog trunk) installed in MyPBX. So if you need to add analog trunks, please make sure that there remain module slots for O2 or SO module first.
The steps to add analog trunks are as below:
Power off or unplug MyPBX.
Unscrew MyPBX, and open the upper case.
Insert the O2 or SO module into the corresponding slot and place back the upper case and tighten the 4 screws. Then power on MyPBX and new analog trunks will be added successfully after rebooting.