The Bell System put its first test call through a laboratory
> Electronic Switching System in 1958 and had a prototype system in
> public service in the early 1960s.
> Would anyone know when other telephone companies, either in the
> U.S. or abroad, developed and implemented their own ESS? For
> instance, when did Automatic Electric put one in service?
In Britain, the GPO trialed an electronic switch at Highgate Wood using PAM/TDM (Pulse Amplitude Modulation/Time Division Multiplex) around 1962. It was not entirely successful.
The first fully operational electronic switch went into service in Ambergate, Derbyshire in 1966, and the GPO also claims this to be the first electronic exchange in Europe. This switch was known as the TXE2 (for Telephone eXchange Electronic), using common control with reed relay switching points.
TXE2 was designed for smaller offices, generally up to a couple of thousand lines. The later TXE4 switch intended for larger offices didn't roll out until the mid-1970s.
-Paul