The paper's former investigations editor, Graham Johnson, was handed a two-month sentence, suspended for one year, which means he may not have to spend any time in prison unless he breaks the law again.
The 46-year-old, who worked at the paper between 1997 and 2005, is the first Mirror Group Newspapers journalist to admit to phone hacking.
He also faces 300 pounds prosecution costs as well orders to complete 100 hours of unpaid community work.
He admitted listening to between 10 and 30 voicemail messages of the soap actress over an "intense but short" period of hacking lasting three to seven days.
More From This Section
The Old Bailey court here heard he was acting reluctantly under instruction from senior managers and although he did not know it was illegal, he realised it was wrong and "walked off the story".
He has since sent a letter to the solicitors of the actress to apologise for listening to her phone messages and using that information for a story.
"The public regard these sorts of offences - quite properly - very seriously," the judge said.
"You are in a different category but the fact of the matter is you allowed yourself in 2001 to behave in this way.
"You could have refused but you did not. You involved yourself in an intense but short period of phone hacking. It is to your credit that you ceased fairly quickly and put that behind you," he said.