The origins and the history of its development are somewhat unclear to me, but following the BTMC 2724 BTMC started on a new design in the late 30s. Anticipating trouble, they made provisions for evacuating their facilities in Antwerp. Sure enough war came, and they quickly brought key people and designs to the UK before Belgium was overrun by the Germans.
From there on they went to the USA to continue their work at one of the ITT facilities there. Right about this time the Federal Telephone & Radio (an ITT subsidiary) model 803 appeared, bearing a close resemblance to the WE 302 and this BTMC 2749. This model was not made for the US market, but for export, especially with Southern America in mind.
And after the war, when everybody had returned to Antwerp and resumed their work the 2749 was introduced.
PTT requested NSEM to design a telephone to conform to the Norm 51 specifications and NSEM, having close ties with BTMC, based their design for the type 1954 on this telephone. The bodyshell and handset are exactly the same.
Besides that, this model was produced by only a very few other ITT subsidiaries and a such not as successful as previous BTMC designs.