The architectural style of the Salt Lake City 1940 Mountain States Telephone & Telegraph (MST&T) main building is well known as one of the “few Art Deco structures in Utah and … a fine example of this style” (McCormick). But the design is only part of the story. The building construction is least as significant: heavily reinforced to support the expected rapid growth of telephone use after World War II with five addition stories and the new heavy automated switching equipment to replace operator-assisted dialing (National Park).

This property on Main and State streets had been purchased in 1928 with the purpose of erecting a new Mountain States operating and headquarters building. Beginning with the 1929 depression, plans were deferred year-after-year, until construction was finally started in 1939. The original structure included three stories – and a full basement – built of reinforced concrete and steel with a terra cotta exterior and highly polished Platt Canyon (Colorado) granite around the base. The austere form, shallow pilaster motifs creating vertical bays, planar elevation with minimal surface undulation, and restrained low-relief ornament are characteristic of the Art Deco style (McCormick). The structure was designed to accommodate five additional stories if needed in the future (Phone company plans two buildings).

Installation of the actual dial equipment was begun by Western Electric in October 1939 and accepted in May 1940. On August 17, 1940 MST&T accomplished their largest flash cutover from operator-assisted to automated dialing. The common-battery (operator assisted) operations in the Salt Lake Wasatch and Hyland exchanges were changed to automated dial systems at this downtown building, as well as the new Ashton & Evans Sugar House structure. The actual conversion of 44,000 phones in five minutes required a second-by-second project plan which was executed by 260 men. The exciting details are well covered in “Conversation starts at the turn of the dial” (1940).

Number changes were necessary on all lines. The “Wasatch” and Hyland” prefixes were dropped, and all new numbers consisted of five digits, such as 5-4150. Customer education was an essential part of the conversion process (Ford).

Ashton & Evans completed two additions to the building: three additional stories in 1947, and a two-story side addition in 1957. The building remains standing (in 2024), has been used continuously by the telephone company, and retains its historic integrity (National Park).