The call, in which 2Day FM hosts Michael Christian and Mel Greig impersonated the Queen and Prince Charles, was made to the King Edward VII Hospital in London where the Duchess of Cambridge was being treated for morning sickness.

Prerecorded on December 4, 2012 and broadcast about 4½ hours later on the Summer 30 program, the call triggered international outrage after Jacintha Saldanha, one of the nurses who was tricked, later killed herself.

The Australian Communications and Media Authority investigated the broadcast and, in a preliminary decision, found the station had used its broadcasting licence in the commission of a criminal offence by recording and broadcasting the call without the employees' consent.

However ACMA's full investigation report remained confidential while 2Day FM took legal action. It sought to have the watchdog permanently restrained from finding it had breached its licence conditions, arguing the authority should not be allowed to make a finding or take action until a criminal court had found the offence proven.

Earlier this month, the High Court ruled in ACMA's favour.

The Herald has now obtained a copy of the final report, which found 2Day FM, owned by Southern Cross Austereo, breached two clauses of the Commercial Radio Codes of Practice. It also said the licensee committed a criminal offence under the Surveillance Devices Act.

The report says the Summer 30 program treated the two hospital workers "in a highly exploitative manner, clearly appearing to purposefully debase them for the enjoyment of others".

Although Christian and Grieg were not expecting to speak to a nurse or to be told information about the duchess's health, station management had time to assess the likely repercussions on both the nurse and the woman who put the call through, before broadcasting.

2Day FM argued listeners in Sydney would not have been able to identify the women, but ACMA said a prank involving "one of the most recognisable women in the world" would inevitably generate widespread interest and the hospital would find out who they were.

This could have placed their jobs in jeopardy and would make them "appear foolish and gullible", the report said.

Further, despite making five additional phone calls to the hospital, consent was not obtained from the hospital or the two employees.

2Day FM argued that it thought a prank call "featuring bad impersonations" would be "humorous and entertaining". It denied the workers were treated in a "highly demeaning or highly exploitative manner". It admitted not gaining consent of the hospital or employees but denied breaching any laws.

In 2Day FM's favour, the report found that, "notwithstanding the clearly tragic circumstances that ensued", the incident was not offensive as to breach decency clauses. And the station did not breach an additional licence condition imposed on it following derogatory and offensive comments by former presenter Kyle Sandilands on The Kyle and Jackie O Show in November 2011.

A spokeswoman for ACMA said the report has been given to 2Day FM for comment and it will not be commenting while that process is underway.

A spokesman for Southern Cross Austereo said the report is a draft and we have been invited by ACMA to submit a response to it by April 7.

"We are in the process of finalising our response and until that time the report remains incomplete," the spokesman said.

ACMA will now consider enforcement against 2Day FM, which may include cancellation or suspension of its broadcasting licence, imposing additional licence conditions, and a referral of the matter to the Director of Public Prosecutions.

For help or information, call Lifeline, 131 114, or visit beyondblue.org.au.