After Elizabeth Edwards hung up without speaking, she woke her husband and told him to fire Hunter.
John Edwards fired Hunter the next morning, but the relationship continued. Elizabeth Edwards, who was battling cancer at the time, switched cell phones with her husband. But to get around this, Young would call to talk to John Edwards and then would three-way call Hunter so they could speak to one another without Elizabeth Edwards finding out.
Young testified that when John Edwards found out that Hunter was pregnant, he was angry and very concerned.
"He said that she was a crazy slut and there was only a one-in-three chance that it was his child," Young testified.
He said in mid-December, in what he compared to a campaign stump speech, Edwards asked him to claim paternity of Hunter's unborn child.
"He talked about how this was bigger than all of us -- getting kids out of Iraq, didn't want Mrs. Edwards to die with this splashed all over the tabloids," Young testified.
Even with the National Enquirer citing the Edwards affair but not naming Hunter, Young said Edwards said the media would eventually lose interest if they thought it was a relationship between two staffers.
"They don't give a s--t about you," Young said Edwards told him. "They want me."
During opening statements Monday, prosecutor David Harbach said that John Edwards had made a choice to break the law.
"If his affair went public, it would destroy his candidacy and he knew it," Harbach said. "He made a choice to accept hundreds of thousands of dollars. ... That is why we are here."
But Edwards' defense team countered Monday that the former lawmaker's actions were not illegal.
"The truth may be a sin, but it is not a crime," said Edwards' attorney Allison Van Laningham. "Follow the path of money. ... The evidence will show it went into the pockets of Andrew and [wife] Cheri Young."
Edwards faces six charges, including one count of conspiracy, and up to 30 years in prison if convicted.
ABC News affiliate WTVD-TV's Anthony Wilson contributed to this story.