For the NextAlarm ABN4A the telephone cabling is the same as in analog connection.
Relating to the OmniPro 2 network connection you would leave the current one in place. IE: the one next to the 5 serial ports would go to your network switch and or router. The ABN4A network connection / port / cable would go to another router / switch connection.
Then you would sign in to your Next Alarm account and put it in to test mode.
Then you would test your OmniPro 2 panel to Next Alarm.
One change in service that I have noticed is that you cannot change your zones et al unless you request to do so via an email. Once you do this once then when you log back in to Next Alarm the assignments of the Zones options are not listed until you do another request via email.
They will enable the feature once. It is sort of PITA.
So in recap your network cabling should be==>
Next Alarm ABN4A ==> Network Port ==> Home network switch or router/switch
OmniPro ==> Network port ==> home network switch or router/switch (as always wired)
Next Alarm ABN4A ==> phone jack == > RJ31X on OmniPro - same as your copper telephone line connection.