Here in the U.K. we've gone from prepay, to postpay, and then back to prepay again over the years, but they've always been dialtone first.
The "AB" box is fondly remembered by older generations and was introduced in the mid 1920s. Payphones, or "public call offices" as they were once called used a modified GPO 300-series desk telephone, fitted to a wall bracket or shelf and wired to this separate coin box. The latter had three coin slots on the top, a return chute at the bottom, and two buttons, one labeled with a very large "A" in a circle and the other with a large "B" in a rectangle (hence the "AB" name). This second button was actually located on the side of the box.
The "AB" phone was prepayment with coin collect and return being done manually by the caller. Dialtone would be heard upon picking up the phone, but calls could not be dialed until coins had been deposited, removing a short from the dial contacts. The coin deposit also applied a short-circuit to the transmitter.
Upon getting an answer, the caller pressed button "A" which collected the coins and restored the contacts to normal, removing the short on the transmitter and allowing conversation to take place. If there was no answer, the line was busy, or the call failed to complete for some other reason, the caller pressed button "B" which returned the coins and simultaneously operated a mechanical timer which opened the line for a few seconds to release any connection. He could also just hangup for a couple of seconds then try again, leaving the coins in situ.
Extra contacts on the dial allowed zero to be dialed to reach an operator without depositing any coins (and as the 999 emergency service came into service the dials were modified to allow a 9 to be dialed with no coins as well). For long-distance calls, the operator would listen for the coins being deposited just as on U.S. 3-slot coinphones, then tell the caller to press button "A" when she got an answer or to press button "B" to return his money if the call failed to complete (after the coin deposit the transmitter would be shorted as on a local call until button "A" was pressed, so the caller was then unable to speak to the operator).
The "AB" coinphone gradually disappeared from most areas during the1960s, but a few survived in rural areas much later. I believe the last one was finally withdrawn from service in a very remote part of Scotland sometime in the early 1980s
STD -- the British equivalent of DDD -- arrived in 1958, and there was a desire to allow direct-dial long-distance calls from payphones without the assistance of an operator. Thus a totally different design of coinphone was introduced in 1959 and gradually replaced the old "AB" boxes as STD expanded during the 1960s.
This was a postpayment phone and an integrated design with handset cradle across the top of the unit, a dial immediately below, and the coin slots on the right (although a separate coin-box only model was also produced to use with regular wall-mounted phones which was common in hotels lobbies and similar semi-private locations).
The old A and B buttons were gone, replaced by signaling from the central office, and a solenoid-operated shutter across the coin slots prevented the deposit of coins until the appropriate time.
Calls -- both local and long-distance -- were dialed first, and when answer supervision was received the office would send a signal to open the coin shutters while applying "pay tone" to the line, a rapidly interrupted 400Hz signal at about three times the normal busy-tone speed (the called party also heard this signal to tell him to wait a few seconds).
After the initial deposit, the charging equipment would simply allow the call to continue for whatever period was appropriate based on the time of day and area called, after which the process would be repeated with another application of pay-tone to request more money. If the caller failed to insert more coins within a few seconds, the paytone would cease and he would be allowed a few more seconds for free to complete the call, after which it would be disconnected and the shutters would close again. The paytone soon became known colloquially as "the pips," e.g. "I'll have to go now, that was the pips and I have no more change." (On the initial deposit, there was no such grace period, so it was pay immediately or be disconnected.)
Now all of those postpayment phones I remember so well from the 1970s are gone too, replaced with modern prepayment types with LCD displays showing credit left and all the other present-day trimmings. Somehow to me they just don't have the character or the attraction of that old equipment.
Below are links to pictures of the two types I've outlined, first the AB "kiosk," then the postpayment type. The latter is an older version, still with lettered dial and slots for 6d. and 1/-. Later versions had numbered dials only and modified coin mechanisms for the change to decimal money in 1971.Paul.