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On April 3, 1973, Motorola engineer Martin Cooper made the first-ever call on a mobile phone, from a street in New York. The device, the DynaTAC, weighed more than a kilogram and took 10 hours to charge for 30 minutes of conversation. Cooper called his rival at Bell Labs to give him the news. The device reached the market eleven years later, in 1984.

On April 3, 1968, Reverend Martin Luther King Jr. delivered in Memphis his final speech before being assassinated the next day — the "I've Been to the Mountaintop" speech, in which he prophetically said he might not reach the "Promised Land" with his people, but that he had seen it from the summit. The following day, a sniper shot him on the balcony of his hotel.

On April 3, 1860, the Pony Express service began — for 18 months connecting St. Joseph (Missouri) with Sacramento (California) through a chain of riders who swapped horses every 15-25 km to cover the 3,000 km in 10 days. The arrival of the transcontinental telegraph in October 1861 made it obsolete. The Pony Express became one of the most romantic legends of the American Wild West.