On April 3, 1973, Martin Cooper, a Motorola researcher and executive, made the first mobile telephone call from handheld subscriber equipment, placing a call to Dr. Joel S. Engel of Bell Labs, his rival. The prototype handheld phone used by Dr. Cooper weighed 1.1 kilograms (2.4 lb) and measured 23 by 13 by 4.5 centimetres (9.1 by 5.1 by 1.8 in). The prototype offered a talk time of just 30 minutes and took 10 hours to re-charge.
On the evening of 3 April, the United Kingdom's United Nations ambassador Sir Anthony Parsons put a draft resolution to the United Nations Security Council.
On April 3, at WrestleMania XXVII, The Rock opened the show by cutting a promo. After appearing in numerous backstage segments, The Rock came to ringside to restart the main event between Cena and The Miz as a No Disqualification match, after it had ended in a draw. As revenge for the Attitude Adjustment Cena had given him on Raw, Rock hit Cena with the Rock Bottom, allowing The Miz to pin him and retain the WWE Championship.
Privately, he wanted to start, but kept it to himself. O'Neal missed games throughout the season due to an assortment of ailments to his right leg including knee, calf, hip, and Achilles injuries. The Celtics traded away center Kendrick Perkins in February partially due to the expectation that O'Neal would return to fill Perkins' role. The Celtics were 33–10 in games Perkins had missed during the year due to injury, and they were 19–3 in games that O'Neal played over 20 minutes. After requesting a cortisone shot, O'Neal returned April 3 after missing 27 games due to his Achilles; he played only five minutes due to a strained right calf. It was the last regular season game he would play that year.
The Rock appeared at WrestleMania 32 where he announced that WWE had broken the all-time WrestleMania attendance record before being interrupted by The Wyatt Family. The Rock got into a verbal back-and-forth with Bray Wyatt before having an impromptu match with Wyatt Family member Erick Rowan. The Rock won after giving Rowan a Rock Bottom and pinning him in six seconds, which set the record for the fastest win in WrestleMania history.
On April 3, 2019, the House Ways and Means Committee made a formal request to the Internal Revenue Service for Trump's personal and business tax returns from 2013 to 2018, setting a deadline of April 10. That day, Treasury secretary Steven Mnuchin said the deadline would not be met, and the deadline was extended to April 23, which also was not honored, and on May 6 Mnuchin said the request would be denied. On May 10, 2019, committee chairman Richard Neal subpoenaed the Treasury Department and the IRS for the returns and seven days later the subpoenas were defied. A fall 2018 draft IRS legal memo asserted that Trump must provide his tax returns to Congress unless he invokes executive privilege, contradicting the administration's justification for defying the earlier subpoena. Mnuchin asserted the memo actually addressed a different matter.