Coulson's lawyer, Timothy Langdale, told jurors they would hear evidence that private investigator Glenn Mulcaire, who has pleaded guilty to hacking phones while working for Rupert Murdoch's News of the World tabloid, had targeted Coulson, the paper's editor between 2003 and 2007.
Langdale asked whether Coulson, who left the newspaper to work for Cameron, could be "both conspirator and victim at the same time."
"The two things do not sit easily together, do they?" he said.
Langdale spoke to the jury after the prosecution finished its opening arguments against Coulson, former News of the World editor Rebekah Brooks and six others on charges stemming from illegal activity at the now-shuttered tabloid.
It is unusual in British trials for defendants to make an opening statement before evidence is heard, and Coulson was the only one of the eight accused to do so. All deny the charges against them.
The prosecution alleges that Coulson, Brooks and other senior editors must have known that phone hacking was being carried out by Mulcaire at the behest of News of the World journalists.
In particular, it says both Coulson and Brooks knew that Mulcaire had hacked the phone of Milly Dowler, a 13-year-old who was abducted in 2002 and later found murdered. The revelation of that act, in 2011, triggered the still-unfolding hacking scandal and prompted Murdoch to shut down the 168-year-old News of the World.
"Clearly, something went badly wrong at the News of the World," when Coulson was in charge, Langdale said. "He wishes he had made some different decisions ... (but) he did not commit these offences. He was never party to any agreement to hack phones."
Coulson and Brooks are both charged with conspiring to hack phones and to pay public officials for information. Brooks also is accused of obstructing the police investigation.
Earlier Monday, prosecutor Andrew Edis claimed that Brooks, then-chief executive of Murdoch's British newspaper unit, hid her notebooks, a computer and other evidence to keep them out of police hands as she was about to be arrested.
Edis said some of the material was only recovered by accident, when a cleaner found a garbage bag containing a laptop computer and other items in a parking garage at Brooks' London apartment building.
The prosecutor said a "media firestorm" was engulfing the News of the World as the hacking scandal erupted in July 2011.
"Brooks knew she was likely to be arrested, and if she was, police would have the power to search her property," the prosecutor told jurors at London's Central Criminal Court.
Edis said Brooks conspired with her assistant, Cheryl Carter, to remove notebooks covering more than a decade from the archive of Murdoch's News International.
And he said she colluded with her husband, Charles Brooks, and with News International security chief Mark Hanna to take material from the Brooks' country home before police could search the premises.
The prosecutor described a cloak-and-dagger operation with touches of a spy film, outlining — with help from recovered emails, mobile phone records and security-camera footage — an operation by security staff to remove a laptop and other items from the country house.
One of the security men later stashed the evidence in a garbage bag behind trash bins in the parking garage at the couple's London apartment — using the delivering of pizzas as cover.
He then texted his superior: "Broadsword calling Danny Boy: The pizza is delivered and the chicken is in the pot."
Edis explained that the "Danny Boy" quote came from World War II movie "Where Eagles Dare."