That $75/month now included unlimited calling as well as texts and probably has some data as well.
The $15/mo was metered service for even local calls, which I would happily go back to. Cell ($10/mo) and VOIP (effectively free) manage the bulk of calling just fine.
Obviously the plan is to move off the copper, to stop getting robbed. But that isn't a justification of the robbers.
I'll note that the involvement here is mainly due to my older father, which is the demographic really meant to be squeezed by this rent extraction.
None of the things that have happened, post deregulation, were impossible to do before, but there was no incentive to do them. A copper line, using either ADSL or SDSL signaling can do anything a wireless signal can, text, data, voice, all at the same time.
What deregulation did was two fold, first it forced the legacy phone company (Bell Telephone, and then the broken up "baby" Bells) to provide access on demand to the copper line, and it allowed private companies to then provide services over that line. New companies were created like Copper Mountain which, under the new options of deregulation, converted "POTS" lines into DSL lines with additional features. The "baby" bells, had to upgrade their networks in order to compete. As part of that upgrade, they needed much more network capacity between their central offices (one copper pair could now host 3 or 4 voice calls, be sending video for example) and much of the late 90's saw miles and miles of new fiber optic networks laid in across the country.
Deregulation also gave phone companies the option of raising their rates without the strict controls of the regulatory infrastructure of "pubic" monopolies, and they sought to recoup their investments in creating new infrastructure by raising rates.
 "Plain Old Telephone Service" - aka a switched, voice only network with one channel per line.
I'll admit their absolute lowest price isn't $75/mo, but $40/mo for "local only". Which I would actually accept, but for caller ID (a modern necessity) being $20/mo on top of that. The whole setup wreaks of gouging a captive market, which effectively describes why I am in this position.
I do fondly remember DSL from Speakeasy/Covad. My point is most CLECs have effectively gone out of business, seemingly due to unbundling going out of fashion and never being applied to coax networks. Although I will say MegaPath remains a great resource for enumerating all services available at an address, the prices will just be at the business level.