Mobile phone records involving a convicted Real IRA member have been accepted as evidence in an Omagh civil action, taken by the victims' families.
The landmark civil action against five men accused of carrying out the Real IRA blast in August 1998 heard that although calls to and from the phone would be examined, their contents could not be revealed.
The bombing, the worst atrocity during the Troubles, injured hundreds and killed 29 people, including a woman pregnant with twins.
Details of a mobile phone which the Omagh families claim Seamus Daly borrowed from Colm Murphy on the day of the attack were highlighted in the Vodafone papers.
The documents also outlined calls from the borrowed mobile to Denis O'Connor, of Kilkenny, on the day of the bombing and some months earlier.
District Court Judge Conal Gibbons, sitting in Dublin, said there was no question of evidence being introduced relating to an intercept of a private discussion in which Daly may have been participating.
There were no family members in court for the rulings.
The groundbreaking action, being taken by six affected families, is the first time the victims of terrorism were confronting the alleged perpetrators and the first time evidence from a Northern Ireland case has been heard in the Republic.
Michael McKevitt, Liam Campbell. Seamus McKenna, Colm Murphy and Seamus Daly all deny any involvement in the explosion.
The civil case will return to Dublin next month when Garda Assistant Commissioner Dermot Jennings is expected to give evidence relating to David Rupert, an FBI informer who infiltrated the Real IRA.