BTW, you should only need a single OBi at each PBX. For each OBi:
OBi PHONE Port -> PBX Trunk
OBi LINE Port -> PBX Extension
Physical Interfaces -> LINE Port -> InboundCallRoute : {pp(ob200123456)}
where 200123456 is the opposite OBi's OBiTALK number.
When the local PBX Extension is called (ringing the OBi's LINE Port), the distant PBX Trunk should see an incoming call (from the OBi's PHONE Port).