It sounds like ABANET has subscribed with Telenet, a X.25 Public Data Network provider, to get access to the X.25 PDN via Telenet. As a subscriber on a PDN, ABANET would have been given a unique address, not unlike your telephone
number, that could be broken down into the world zone, country zone, a network digit and network terminal number.
Therefore, to reach ABANET from another X.25 PAD, like MacX25, you just need
their address. From MacX25 you enter that address in the "Host Address" or
"Called Address" field. Then, open the connection via a terminal communication
tool (MacTerminal 3.0, White Pines Mac241, or the like). Their address will be
understood by your local PDN provider's packet-switching equipment and your
call request will be routed through whatever PDN networks are required to
reach ABANET.