With a "Left" office FXO port connected to a "Right" office FXS port (purple connection), and a "Right" office FXO port connected to a "Left" office FXS port (orange connection), users of the two FacetPhone systems can call each other through the network.  In addition, the users of each system can make out-going calls using the trunk lines of the "other" office. With the "Left" office interconnect FXO port defined as Trunk Group 1 along with its interconnect FXS port defined as Station 101, and the "Right" office interconnect FXO port defined as Trunk Group 1 along with its interconnect FXS port defined as Station 101, then users in the "Left" office can become Station 101 of the "Right" office system by dialing  8 1,  and users in the "Right" office can become Station 101 of the "Left" office system by dialing  8 1.  After a "Left" office user dials  8 1  they'll get a dial-tone from the "Right" office system.  Then they can either dial a "Right" office extension or dial  9  and a phone number to call out using "Right" office trunk lines.  Likewise, a "Right" office user dialing  8 1  gets a dial-tone from the "Left" office FacetPhone system.  They can then dial a "Left" office extension or dial  9  and a phone number to call out using "Left" office trunk lines. Note, callers of either office can also reach the "other" office by dialing their FacetPhone system's interconnect station, but the call will come in on the "other" system as an outside call and as such, at that point can only dial an extension of the "other" system, not use the "other" system's trunk lines..