The Dallas "Main" central office serves Southwestern Bell (SBC) as the main regional tandem and AT&T for long distance and toll services in the Dallas Texas region. The office was originally built by Southwestern Bell in the 1920s. Dallas became an AT&T Long Lines microwave hub when TD-2 microwave service was introduced in the early 1960s. Phoenix was a regional center in the hierarchy switching plan and had direct trunk groups to the Denison, Longview and Houston primary offices and trunks to the Oklahoma City, Ft. Worth, San Antonio and Sweetwater sectional offices. Original L-3 coax cable connected Dallas to Ennis, Kaufman, Adams, Ft. Worth, san Antonio and Cisco. AT&T introduced 4ESS service to the office in 1976 (Dallas 3) and 1981 (Dallas 4). Today the CO has major fiber connections to Plano, Irving, Tulsa, Oklahoma City, Ft. Worth, Abilene, Houston and Austin.

Microwave paths from Dallas were: Grapevine, Adams, Terrell, Midlothian and Forth Worth Junction.

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