Como o cliente de lançamento, a United Airlines queria isso. De fronteiras da Boeing :
The 720 was a ... first marketed to the airlines as the model 707-020. United Airlines was very interested in the 707-020 but had previously decided to go with Douglas and the DC-8. To help United avoid any negative public relations for going back to the 707, Boeing changed the name of the 707-020 to the 720.
De acordo com a aviationweek , a mudança de nome ocorreu a pedido de William 'Pat' Patterson, o presidente da lançar o cliente United Airlines.