The original 3-slot payphone, where coins dropping rang bells to
> indicate amounts, is now seen only in old movies. It was a very long- > lasting design.
> In the 1960s the Bell System developed a replacement model that would
> be more efficient, suitable for automation, and more vandal resistant.
> It contained a single slot for coins and was in a boxy shape.
> Originally introduced in high demand locations, it eventually became > the standard.
> Externally at least, the single slot phone offered by the baby Bell
> successors, looks the same. Many still say "BELL SYSTEM Western
> Electric" on some part. They have real mechanical ringers, not
> However, I presume the innards, even of basic models, are more
> advanced than that of the 1960s model.
> For the basic models in baby Bell service, would anyone know if there
> are significant changes from the 1960s version? Or, are they just
> using old units that they have a large inventory of?
Yes, the inner workings have changed somewhat and the way the phone signals the network or the operator is different. Originally the phones emitted "deedle" tones one deedle for a nickle and two for a dime and five for a quarter unlike the three-slotters which had a ding for each nickle or two dings for a dime and a bong gong for a quarter. The later 1A1 (single slotters) had relays which signaled the operator on their consoles or let the automatic equipment know that you had deposited the correct amount of coins.
Modern 1A2's in some areas such as Bell South's territories have all been "COCOTised" i.e. they are no longer central office controlled.
The new "smart" phones such as the Millennium marketed by Nortel are also chip controlled rather than CO controlled. The Millenniums also can take payment in multiple ways with coin, credit card or with a smart card with a chip in it.
This site has a lot of information on the fortress: