Asked to name his enemies, Shell named Smith.
Both men had been vying for the same woman, whose name has not been publicly identified.
Smith won - then lost in more ways than one.
For more than an hour Monday, he stood before the judge answering routine questions about his background, struggling to hold back tears. He and his lawyer, William J. Brennan, said they would say more about the crime at his sentencing.
In an interview that aired Friday on the ABC newsmagazine 20/20, Smith said the woman was his co-worker at 3 Brothers Pizza and Pasta in Port Richmond. He and Shell, a Texas transplant living in South Philadelphia, had never met but traded nasty text messages.
When the girl ultimately chose Smith, Shell allegedly retaliated by posting a naked photo of her online. Smith sought revenge.
"I wanted him to pay for what he did," Smith said in the interview.
Using a payphone and a fake name, Smith called airport police and told them Shell was carrying drugs and liquid explosives aboard the United Airways flight.
Smith said he wanted to inconvenience just one person, but acknowledged the impact was wider.
His actions, he told the news program, were "completely moronic."
Smith's plea was never in doubt. Agents found him at work the same day of the hoax and confessed, according to an affidavit from Special Agent David L. O'Brien of the Bureau of Alcohol, Tobacco, Firearms and Explosives.
In November, prosecutors filed charges through an information in the case, an indication that a guilty plea was forthcoming.
The prosecutor, Assistant U.S. Attorney Jennifer Arbittier Williams, said Smith's plea deal calls for him to reiumburse and write letters of apology to each passenger on the flight, and pay the airline and emergency personnel for the cost of the response.
The total could top $20,000.
In the end, neither guy got the girl, according to Smith. "I love her with all I have," he said during the interview, but she dumped him anyway.
Contact John P. Martin at 215-925-2649, at firstname.lastname@example.org or follow @JPMartinInky on Twitter.