Almost 3,000 people lost their lives in the atrocity on 11 September, 2001 and bosses at financial services company Cantor Fitzgerald now hold an annual charity event to raise funds for good causes after two-thirds of their workforce perished in the North Tower of World Trade Center.
On Tuesday, famous faces took to the trading floor to man the phones, with profits from every transaction going to the charity of their choice.
Rapper 50 Cent, who was among the participants and manned the phones for three hours, tells New York Post gossip column Page Six, "I am honoured to come and be a part of this... I try to promote conscious capitalism and to connect my business to giving back so (other artists) see the example and follow."
Tennis star Venus Williams and Olympic swimmer Ryan Lochte also took part, along with American football star Victor Cruz, whose father was one of the firefighters called to Ground Zero on the day of the attacks.
The New York charity drive raised more than $12 million (£7.5 million) and the good work continued across the Atlantic in Britain at the offices of Cantor Fitzgerald's sister company BGC Partners in London's Canary Wharf.
Leona Lewis, Joan Collins, Sir Roger Moore and Richard E. Grant took part in the London leg, along with singer Sophie Ellis Bextor, Formula 1 ace Lewis Hamilton, British royal Princess Beatrice and her mother Sarah Ferguson, and Olympians Mo Farah and Dani King.