Trimphone

It was positioned as a more fashionable alternative to the standard telephones available from the General Post Office (GPO), the nationalised predecessor to British Telecom.

The luminous dial or betalight contained the mildly radioactive element tritium, which later caused some concern about safety.

In June 1991, the United Kingdom Atomic Energy Authority at Harwell was fined £3,000 by Wantage Magistrates Court for accumulating radioactive waste, having collected several thousand Trimphone luminous dials in a skip.

Consumers were divided as to its aesthetic merits and some models required rewiring to connect to the public phone network in the UK.

The first example of the Trimphone was presented in May 1965 by the Postmaster General, Tony Benn, to a newlywed couple in Hampstead in a ceremony marking the ten millionth telephone to be installed in Britain.

This effect came from a small glass tube of tritium gas, which gave off beta radiation, which in turn energized light-producing phosphors and made the dial fluoresce.

An MF4 (Touch-tone) design had to await the development of an integrated circuit to replace the bulky coils and capacitors otherwise needed.

A Trimphone, viewed from the side. The handset cradle functioned as a carrying handle when the receiver was off the hook, and the coiled cord in theory allowed the phone to be carried around.
The Trimphone, from above, in the original dial design and the later keypad. To fit the electronics used to generate the dial pulses (and in later models, tones), the depth of the case was increased.
The Telephone No. 712 usually featured an alphabetical dial, which was also used on early versions of the 722.