1889 W. H. Preece & J. Maier Telephone 249 This switchboard is required to distribute the trunks between the different offices [sc. exchanges], and also to enable the testing of all the trunk and subscribers' lines to be carried on from one central point.

1908 Jrnl. Inst. Electr. Engineers 41 120 In America the local term remains the same, the junction is called ‘trunk’, and our trunk is called a ‘toll’ or ‘long-distance’ line.

1921 W. Aitken Automatic Telephone Syst. I. 4 The designation of the lines interconnecting apparatus at different switching stages..is somewhat confusing. The American generally speaks of these as trunks, which practically is equivalent to our junctions... For example, the circuits between first and second preselectors,..second and third selectors, and third selectors and connectors, are all trunks or junctions... Very commonly the lines between exchanges in this country [sc. Britain], and for the use of which an extra charge is made.., are known as trunks. For these the American terms toll line or long-distance line is used.

1925 C. A. Wright Telephone Communication ii. 33 It is necessary in central-energy systems to serve districts of more than ten thousand lines by means of a number of central offices connected by trunk circuits or trunks.

1966 McGraw-Hill Encycl. Sci. & Technol. (rev. ed.) XIII. 433/1 When the extension user dials the first digit, the wipers of the first selector step upward to the level corresponding to the digit dialed, and automatically step around in a horizontal arc..until they find an idle trunk.

1978 Sci. Amer. June 90/2 A modern telephone exchange is connected not only to its own subscribers but also, through special lines called trunks, to other exchanges serving other subscribers.

1978 P. H. Smale Telecommunication Syst. I. vii. 60 There are various grades of exchange in order of importance... There are also various grades of interconnecting line, for example subscribers lines, junctions and trunks, and again the number gets fewer as length, importance and cost increase.

1889 W. H. Preece & J. Maier Telephone xx. 353 As the trunk operators had too much to do..a special plan was arranged by which a subscriber requiring a connection to another town mentions the word ‘trunk’ to the ordinary operator.]

1947 N. Cardus Autobiogr. iii. 233 He rang me up at my Manchester house; he was speaking from Harrogate. When ‘trunks’ gave me notice of his call I expected something urgent.

1977 C. McCullough Thorn Birds ix. 203 Give me trunks, please, switch... I want to put an urgent call through.