You need to acquaint yourself with the history of the Bell System.
Every extension, lamp, headset jack, signal button, buzzer, winking feature, and bell-cut-off key were billed separately and perpetually. (Long cords, and colored phones, were only billed once.) These recurring business charges subsidized, through a convoluted accounting procedure, the concept of residential "universal service" to every household in the country, and kept long distance charges manageable.
"Money could not have been that tight" you say? Do you think a farmer, even a few miles from the nearest central office, would have been capable of paying the line construction costs to set 40 poles per mile, and string just a single pair of wires to get basic residential service? The money WAS tight, but businesses in far-away cities paid the 30 cents per month to pay for Farmer Jones' black 302 set.
Without the $.30 per month charge for a winking Hold lamp, multiplied times five zillion key sets, your grandma and grandpa would never have been able to afford to call and wish you a Merry Christmas.
I am not a complete apologist for the way the company was run, I just can't see any other way of having done it.
See:
"Monopoly" by Joseph C. Goulden
for a start.
Then get a copy of the USOC handbook, issued to business office employees and installers. It lists every item that a subscriber could order and pay for.
The breakup of the System was precipitated by a false sense of doing good by well-meaning (?) government officials who just couldn't stand the way the whole "shady" accounting was being done.
Also Google "consent decree Bell System"
