Trimphone

The Trimphone is a model of telephone designed in the 1960s in the UK. It was positioned as a more fashionable alternative to the standard telephones available from the GPO, the predecessor to British Telecom. The name is an acronym standing for Tone Ring Illuminator Model, referring to the then innovative electronic ringer ("warbling", as opposed to the traditional bell) and the illuminated dial. The luminous dial or betalight contained the mildly radioactive element tritium, which later caused some concern about safety. At one point during the 1990s the United Kingdom Atomic Energy Authority at Harwell was fined £5,000 by Wantage Magistrates Court for accumulating radioactive waste, having collected several thousand Trimphone luminous dials in a skip.

Although a later model featured buttons that did not light up instead of the original dial, it continued to be known as the Trimphone. Consumers were divided as to its aesthetic merits, and some models required rewiring in order to connect to the public phone network in the UK.

The innovative design by Martyn Rowlands for Standard Telephones and Cables (STC), won a Design Centre award in 1966. It originated from an initial idea in 1959 for a luxury telephone to add to the Post Office's range. Towards the end of 1963 they chose this design although they considered others including a submission from GEC. In 1964 the GPO placed a contract for 10,000 units.

The Trimphone started life in 1964 as the Telephone No. 712. The Telephone No.712 was usually supplied as a 712L with an alphabetical as well as numerical dial. The Trimphone was the first in the GPO range to use a tone caller which warbled at around 2350 Hz modulated by ringing current. The volume of the ringer gradually built up over the first few cycles. There is a volume control in the base of the telephone with 'loud', 'medium' and 'soft' settings (a silent setting was achieved by slackening off a screw on the tone ringer board inside the phone).

...
Wikipedia