History - Bell System rentals for PBX equipment? [telecom]

Is anyone familiar with equipment rentals charged by the old Bell System (pre-divesiture)?

Over the years, the Bell System offered several models of equipment that were developed at different times, but performed essentially the same way for the average customer. I was wondering how Bell charged for various equipment.

EXAMPLE 1:

Let's imagine a small business that uses a manual PBX and needs a cord switchboard. It has five trunks and thirty extensions. In the 1970s, such an organization could have been served by the following cord switchboards:

--551, a pre-war unit. It was still in widespread use in 1970.

--555, a post war unit. While the keyshelf was slightly different, it was functionally the same as the 551.

--608, a 1960 unit. It had automatic ringing and recall and a more modern appearance, although these features would be of limited value to a light traffic PBX.

Would Bell have charged the same rental for the 551 as the 555, given they were functionally the same? Would there have been a premium for the 608?

EXAMPLE 2:

Let's a imagine a small business that has uses a dial PBX, with only basic features. It has eight trunks and fifty extensions. In 1970, such an organization could've been served by a variety of dial PBX equipment of various generations designed for small customers, including SxS, crossbar, and ESS.

Further, a variety of switchboards would be available to serve as the attendant's console. Some were modern cordless desktop models that looked like a Call Director. These were more productive since ringing, recall, and disconnection was automatic, were attractive, and were very popular. But customers could, if they chose (as some did), to utilize a cord switchboard designed for dial service, such as the

552, 556, and 608.

--740 (various models, step by step)

--756 (crossbar)

--757 (crossbar)

--770 (crossbar)

--800 (ESS)

--805 (ESS)

--761 (crossbar, designed for motel service)

Did Bell charge different rentals for the various models of dial equipment, even if functionally similar to the customer? How about for the associated attendant's switchboard?

[public replies, please. thanks.]

Historically, there were different schemes, but by the 1960s Ma had pretty much settled on the "Series" method of charging for PBXs. A company would order a PBX system and pay a tariff rate based on the series. A Series 100 was basic dial tone around a building. Series 200 added, I think, a nicer operator console. Series 300 added a few modern features, like the ability to transfer calls.

How it was implemented, though, was up to Ma. So the old 701 Stepper and 551D cord board might be used to do Series 100. The 770 was a smallish (400 line, IIRC) crossbar that could do Series 300, but they'd put a different model in if they thought the subscriber might grow beyond its size.

After Carterfone, they started getting more competitive, and tariffed specific products. Dimension, their analog-SPC PBX, came out around

1976 and was the only series under tariff; they kept Antelope (System 85, basically "digital Dimension") off the market until 1983, when it was available untariffed from ATTIS, even though it was designed and "in the can" by 1979. Series may have been grandfathered during that era.