A Bell System advertisement in the July 9, 1971 LIFE magazine describes emergency call boxes being installed on a remote stretch of I-80.
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(two pages)
(I don't know if they're still there.)
Also in 1971, Bell announced discounts for dialed-direct long distance calls, and at certain times, a one-minute minimum time instead of three minutes. If direct-dialing was not available, discounted rates still applied to basic operator calls.
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(two pages)