Well, if we're talking about connectivity via CorNet here, this is it in a nutshell... (I don't know the 4800 so I'm working off a quote I have).
You probably need a DIU2U digital trunk interface card for the 4800 - I believe buying the card licenses it on that platform but not sure. Then, assuming by series 80 you are referring to the 9751 Model 80 running 9006 software, you need a TMDN or TMDN64 card depending on your software release that needs to be plugged into a slot that is programmed for it (wired for), you need to have licensed the RolmNet software, probably SatOps and have sufficient licenses for the trunk ports, etc. Then you connect the 2 sites together with a DS1 circuit (T1) using the CSU's and other required cables, etc.
That gets your hardware connected together. Now you have to create a trunk group on both sides, create a route pointing to the trunk group, and point your extensions or other traffic to that route so they go across to the other side. It works rather slick, passes caller-id, allows auto-callback and several other functions.
In my case my voice WAN is set up hub and spoke. All the remote sites tie back to the main site in the center that knows who everyone is and where they go. All the remote sites are set up so if they don't know who it is they send it to the main site for routing. In the event one of the links fails we can still call between sites with 7-digits, so it's no big deal other than they lose access to PhoneMail which is sitting out in the middle. All of my remote sites have their own trunking to the world so all sites can survive independent of the others, and if the outside trunking fails to one of the sites I can fail those trunks over to the main site by making a phone call to activate the disaster plan, and I can route their traffic across the private network (albeit congested) until the problem is resolved.
CorNet is pretty cool in my humble opinion!