Actually, the question is very reasonable. Since the 1980s the nature of the public switched network has drastically changed and much of that material is obsolete. Here's why:
1) Expense: The "trunk" (physical connection) between two central offices was extremely expensive. It consisted of (a) switchgear on the front end, (b) the physical wire, and (c) switchgear on the rear end. Accordingly, trunks between offices rationed and carefully planned -- just enough to meet demand but not more so. The phone company worked hard to maximize capacity of the physical wire (carrier circuits) and switchgear.But after the 1980s the costs dropped dramatically. The head and rear terminal equipment became cheap. Fiber optic with very high capacity replaced copper and coax. Suddenly capacity was not a big an issue anymore. Everything was so cheap there could be waste.
2) Politics: The old model had the Bell System handling everything. The 1983 model had the local Bell companies handing off toll calls to dedicated toll carriers (AT&T, MCI, Sprint, etc.)But further deregulation allowed local companies access, too. Bell (that is, successors to Bell) might own the physical line between your house and the C.O., but once inside it was immediately handed off to a new company that did the switching instead. (Bell had to spend a fortune building extensions to C.O.s to house lockable rooms for new switchers).
Non-Bell companies might lease lines and switching from Bell or own their own. Bell might lease stuff from non-Bell companies, indeed, they often now sub-contract out repair and installation work. (If you see a plain truck with a small stick-on Bell company sign instead of fully painted, that's probably a sub contractor.)
3) Many people use their cell phone or cableTV phone as their line. The routing is completely different for those systems. 4) New services: We have new stuff like DSL and FIOS.So, the question of routing methods today is quite reasonable and realistic. With so much deregulation, it is also relevant to know if a given carrier, even a "main" one, is good to use.
Where would you suggest to research to get _current_ information appropriate for a lay person?