"I was starting to worry when I hadn't heard anything," explained O'Callaghan, who was surrounded by Munster's aspiring professionals and fellow Heineken Cup winner O'Leary as the Sky Sports announcement grew near.
"I know they told us how it would be done but still I thought 'yeah right - there will be some bit of word before that'. But no, nothing.
"So I was there with the Academy boys, me and O'Leary, and I'm thinking, this isn't the place to be. What'll I do in front of these lads if I'm not picked."
Fortunately for O'Callaghan, that wasn't something he needed to worry about as his name was eventually read out along with those of seven Munster colleagues.
O'Leary, on the other hand, was sure his chance had passed him by after the names of two other scrum-halves were read out before him.
"Then Gerald Davies starts to read out the names and when he calls out Mike Phillips, Harry Ellis, Leary goes, 'Oh no', thinking that's his chance's gone cause they'll just bring two nines," added O'Callaghan to Munsterrugby.com.
"But straight away his name is called and he's jumping up and down going 'Yeeeeees'.
"My case wasn't helped when they switched channels just after that but they switched back just in time for me to hear my name and, ah well, I was just delighted.
"But after that you think of the lads not selected, teammates, and realise just how lucky you are."
A third Munster player, Ronan O'Gara, took a different approach when it came to learning of his Lions fate.
O'Gara toured with the Lions in 2001 and 2005 and attempted not to watch or listen to this year's announcement, preferring instead to wait for others to inform him of his inclusion or non-selection.
Having gone down to Musgrave Park with Doug Howlett to practice his kicking ahead of tonight's Magners League clash with the Scarlets, O'Gara finally gave in to the urge to listen live as the 1.30pm announcement came ever closer.
"I said to Dougie, 'come on, into the jeep, turn on the radio', and I heard it there," said O'Gara, who was one of two fly-halves named in the 37-man party.
"It's my third trip but you never take anything for granted in this game. I'm delighted of course, delighted for everyone and at the same time gutted for a few of the boys, Marcus (Horan), John (Hayes) and Leams (Denis Leamy), who didn't make the cut."