But he soon realised the source of the call was the Vatican, and not long after found himself talking to Pope Francis.
Argentina's Alfredo Leuco is not the first person to be called by the pope.
It is reported that the Holy Father admired his work and the journalist came to his attention after publishing an open letter challenging the Pope's decision to receive Argentine president Cristina Kirchner for a fifth time in the Vatican. Leuco wrote that many Argentines were "upset or disillusioned" by the meeting.
He said: "On Saturday I was celebrating my birthday with six of my best friends and partners in the city of San Pedro.
"At 11.23 I got a first WhatsApp from Monsignor Guillermo Karcher. I thought it was a joke. But when I noticed the number of origin was the Vatican," Leuco said on his radio programme.
"I had to pinch myself several times to make sure I was not dreaming. I was filled with happiness when he said: 'The pope remembers you and greets you'."
That afternoon it was reported that he had a voice mail from the Pope on his mobile and an hour later the Pope rang again.
Leuco's letter had caused controversy in the country and the journalist had been criticised on social media. The pope praised the "moral fortitude" of the letter.
He said the pope ended the conversation saying: "I wish you a good birthday party and do not forget to pray for me."
"I did not dare to tell him that I knew not how to pray." He then was taught how to pray so he could fulfil the pope's request.
On his blog he later wrote: "I say and I repeat and still I cannot believe it. But it is absolutely true. Wonderfully true.
"This is the greatest achievement of my journalistic life: Pope Francis did me the honour to answer, with great affection and gratitude, the open letter read on this radio that had such an impact that it became one of the most discussed topics on Twitter."
