Joey Amour Jackson and Lance Riddle — also known as “Apeshit” and “C-Port” — masterminded the scheme while locked up in the US state of Georgia.

The pair used contraband mobile phones to call members of the public, while using specialist software to make it appear they were calling from local police departments.

Victims were told they had missed jury duty and were therefore required to pay substantial fines by buying gift cards or making wire transfers, otherwise they would face arrest.

At least 119 victims were parted from more than $464,920 (around €398,000 or £345,000) as a result of the scam, the US Department of Justice said.

With the help of co-conspirators outside prison, the stolen proceeds were used to pay off personal debts such as house and vehicle loans, as well as to purchase drugs.

The two prisoners were convicted on Friday of conspiracy to commit wire fraud and conspiracy to commit money laundering.

They now face decades in federal prison without possibility of parole.

Paul Brown, the FBI’s special agent in charge in Atlanta, said: “Not even prison cells prevented these criminals from harming dozens of innocent people.

“Hopefully, this verdict will bring some level of comfort to the victims and prevent others from falling for similar scams.”