In 1886, it built an ornate red brick and terracotta building 19, Newhall Street, now grade I listed, for its Birmingham Central exchange, opened in 1887.

The building still bears the company's NT logo and some cherubs holding what appear to be old style telephone handsets.

With the policy of amalgamation, the NTC, under the direction of William E. L. Gaine as general manager and Dane Sinclair as engineer in chief, set about creating a uniform organisation over eight districts; Metropolitan, Southern, Western, Midland, North-Western, Northern, Scotland and Ireland.

In 1901, the Postmaster General and the NTC signed an agreement to prevent unnecessary duplication of plant and wasteful competition in London.

In 1905, the Postmaster General and the NTC signed a further agreement for the purchase of the NTC's system on the expiry of its licence on 31 December 1911, an option for the Post Office that formed a part of the original licence agreement of 1881.