Around the time of divesture it was said the telephone rates would be restructured to match cost against usage. Thus we saw new charges for
411, operator assistance, wire repair, etc.At that time they also predicted the end of flat rate service on the grounds that some people used it very extensively while others used it sparingly. In the 1980s the telephone was used more than ever, along with businesses operating from home and home computers. As you noted, some places did eliminate flat rate plans. As a big phone talker, I was concerned.
But the explosion in technology -- cheaper switches and line terminal eqiupment, fibre optic lines -- made it possible to hold the line on some rates and eventually offer national unlimited. Admittedly, my national unlimited is only a few dollars more than metro unlimited.
Undoubtedly the phone company was concerned with the use of computers on voice lines and the heavy usage of equipment. But many people with computers got second or third phone lines just for the computer, which offset the cost. Now of course people are shifting to dedicated lines like DSL. (What happened to ISDN?) Verizon is pushing FIOS like crazy even though they holding back installing it in apt complexes.
In any event, in thinking about the movie, so much has changed in telecommunications. Think about how Woodward and Bernstein would've done things differently with cell phones, fax, and the internet, as well as Deep Throat and the efforts to identify Deep Throat. Indeed, just by 1980 (six years) things had changed a lot.
From a _technological_ point of view, I never understood Watergate. (Let's leave politics and Nixon out of this). The Watergate scandal wasn't about the Watergate Apt breakin, it was about numerous other wiretaps that were "illegal" and then the effort to cover them up. But if Nixon's people wanted to wiretap, why didn't they just ask the friendly compliant phone company to do so under "national security"? AFAIK, the phoneco cooperated with such requests and didn't ask questions. Indeed at that very time the phoneco was working with the Justice Dept to help track down Blue Box users.
Or, by that time, the technology existed to just add a recorder external to the drop line on the outside of a building and no one would know about it.