The Sunday Mirror carried out phone hacking "on a fairly grand scale", a former reporter at the newspaper told a trial at the Old Bailey yesterday.
Dan Evans, 38, said phone hacking went on for several years at the tabloid, where he learned how to intercept voicemails during a "secret" meeting with another journalist.
Evans, who also worked at the News of the World, pleaded guilty last year to phone hacking at the Sunday Mirror.
He is the first person to plead guilty to phone hacking at any newspaper other than the News International title, which was closed three years ago. The jury was told Evans admitted hacking at both Sunday tabloids, as well as conspiracy to commit misconduct in a public office and making a false statement.
The court also heard he entered into a written agreement with the Crown Prosecution Service last year, as a result of which he was appearing as a prosecution witness.
Evans said when he was given a staff job at the Sunday Mirror in 2003, he was taken into a room and told he would be discussing "something which was a secret". He said: "It was to show me how to hack a voicemail for the first time. There was a bundle of pages with famous people's names and phone numbers on and they said, 'this is your job, you have to hack and crack the voicemails of famous people'.
"I had been tasked to hack people's phones on a fairly grand scale," Evans said.
He said he met Andy Coulson, the News of the World editor, with whom he discussed phone hacking as a method of getting stories.
Evans said: "I said I had been breaking big exclusive stories cheaply, which was the 'kerching' moment. Big exclusive stories cheaply equals job.
"I said there were two ways of doing that: one was to spend a lot of time doing an investigation, the other was to dial up somebody's phone call lists, work out who they are having relationships with, listen to voicemails ... and you've got something that's going to shift units from supermarket shelves. Andy seemed really pleased."
Coulson denies charges relating to phone hacking and alleged corrupt payments. Seven other defendants deny all charges against them. The trial continues.