In 1965, AT&T introduced its first redesign of the pay telephone — the single slot, flat fronted 1A1. The design remained mostly the same until the 90s. There were a few types of the 1-slot phones, determined by the control board and its 3-character code:

• 1st character: 1 = surface mounted, 2 = flush mounted (panel phone), 3 = electronic^*1
• 2nd character: a model code. A = CF only, C = CF/DTF, D = DTF only, E = postpay^*2
• 3rd character: 1 = rotary, 2 = Touch Tone, 3 = manual

^*1 3A2-3 type was never really seen. Announced in 1984, resembling the Millennium, controlled by microprocessor.
^*2 1E types were only made in rotary and manual, not TT.

CF = Coin First (initial deposit was required to hear a dial tone start dialing, usually initiated by a ground start ^{[citation needed]}
DTF = Dial Tone First. User can dial the first three digits without a coin (this is controlled by a Central Office equipment). A collection of initial deposit signaled to CO by applying a resistance between Tip and the ground. Initial deposit amount was determined by the mechanical totalizer (A and C type) and electronic totalizer in D (on the controller board).

1A boards: line polarity matters and must not be reversed upon call answer
1C boards had two 11-pin round connectors and all analog circuits, while 1D had one 11-pin (dial unit, headset) and one 13-pin D-sub for totalizer.

Various makes (revisions) existed for each set over time, actual board type for 1C set was 31 series, 1D - 32A/B/C.

1D - 32B board, 1984. Manufactured from late 70s. Notice the mercury relays. There are two “sandwiched” circuit boards, the back side has five dip switches to select the initial rate (5+10+20+40+80, selected: 50ct). 32A board was almost the same, except the dip switch on the back was not present - rate was determined by a wire connection matrix.

1D - 32C board, 1989. The last one from the original 1D series. It only has one layer and the rate switches are on the top. There is a newer version with a MOSFET instead of one of the relays.

Original 1D (“dumb”) boards were only made until certain year^[when?]. In the 90s they were being repaired or replaced as needed with “retro-fit” microprocessor boards, mostly Protel 4000 and 8000, Elcotel, GTE Supply and other OEM boards.

1C2 payphone, 1975, 31A board and 20A coin sorter. Mechanical totalizer visible in the middle.