@OBT

do you think connecting in series will do the trick?

=phone line ---- PBX 1
====================L1-- Ext line 1
====================L2-- Ext line 2
===========================up~
===========================to~
====================L23-- Ext line 23
====================L24-- PBX 2
==============================L1-- Ext line 25
==============================L2-- Ext line 26


Hello