The 66-year-old, from the city's Marconi area, woke up to the first call to his landline at around 6am.
“I could hear the sound of the sea, but I didn't understand a word of what was being said,” he told Corriere.
“It was someone speaking a little English, a little French. I didn't understand what he wanted at that time of the morning.”
Not realizing that the person at the other end of the line was a migrant, who was on a flimsy boat crammed with others making their way from Libya to Sicily, the pensioner hung up, only to be called again. And again.
Frustrated at not being able to understand the person at the other end of the line, and worried that he was a crank caller, the pensioner's own SOS was picked up by officers on duty at San Paolo police station.
Two policemen went to the pensioner's home, where the calls were still happening.
At first they too thought it was just a case of phone harassment, but the pensioner himself began to suspect it could be a call for help, possibly from someone who was about to commit suicide.
Finally, after several more calls, during which they could hear the sound of waves, strong winds and a boat engine, they realized the calls were from a distressed migrant.
An officer at San Paolo station told The Local that they were able to trace the number back to a satellite phone, which are usually given to migrants by people smugglers with instructions to call the sea rescue service's Rome operation as they approach Italy.
"The caller tried lots of numbers at random with the Rome prefix, until the pensioner answered," the police officer said, adding it is thought an Egyptian man made the call.
"It was hard to understand the message, as he was speaking mainly in English and French, and just a little Italian."
The Italian Coast Guard was immediately alerted, and four boats, heading towards Sicily and carrying 600 migrants between them, were located.
The migrants were among the almost 1,500 rescued off Sicily over the first couple of days of this week.