Prosecutor Andrew Edis said ex-news editor Greg Miskiw, ex-chief reporter Neville Thurlbeck and former reporter James Weatherup all entered guilty pleas before this week's high-profile phone hacking trial of former News of the World editors Rebekah Brooks and Andy Coulson, who are in the dock along with Brooks' husband Charles and several others.
Private investigator Glenn Mulcaire, who had already been convicted of similar offences back in 2007, also pleaded guilty.
Brooks and Coulson, both 45, deny a variety of phone hacking-related charges.
Speaking during the trial's opening arguments, Edis said the guilty pleas show "there was a conspiracy which involved a significant number of people."
Edis said Brooks and Coulson must have known about phone hacking by staff under them because "they controlled the purse strings" and signed off on illicit payments.
Brooks and Coulson face charges of conspiring to intercept communications — phone hacking — and conspiring to commit misconduct in a public office, which refers to illegal payments to officials.
Former News of the World managing editor Stuart Kuttner and ex-news editor Ian Edmondson also are charged with phone hacking — in conjunction with Brooks, Coulson and others — over a period stretching from 2000 to 2006.
The paper's former royal editor, Clive Goodman, is charged with conspiring to commit misconduct in a public office alongside Coulson.
Brooks, her husband Charles Brooks, her former assistant Cheryl Carter and former News International security chief Mark Hanna are charged with attempting to obstruct the phone hacking investigation by withholding documents, computers and other equipment from police.
The hacking case — which is not expected to end until well into next year — is the first big criminal trial spawned by the 2011 revelation that the News of the World had hacked the mobile phone voicemails of kidnapped 13-year-old Milly Dowler, who was later found murdered. Brooks edited both the News of the World and its sister paper, The Sun, and was chief executive of Murdoch's British newspaper division. Coulson also edited the News of the World before becoming communications chief to Prime Minister David Cameron.
The hacking scandal first exploded in 2006 following revelations that the News of the World eavesdropped on members of the royal household. But it resurfaced in 2011 following the Dowler revelations, leading to dozens of arrests and resignations. The renewed scandal rocked the British establishment and led Murdoch to shut the 168-year-old newspaper.
Photographers have clustered outside the court, known as the Old Bailey, since the trial began on Monday. More than 60 journalists are covering proceedings from the courtroom and an overspill annex.
Edis urged jurors to put aside the copious pre-trial publicity surrounding the case, saying Wednesday the issue they had to consider was a simple one.
"There was phone hacking," he said. "Who knew?"