"What are the nuns doing that they can't answer?" the pope joked in his message to the Carmelite community in Lucena. "I am Pope Francis. I wish to greet you in this end of the year. I will see if I can call you later. May God bless you!"
The nuns sent the pontiff's message to a Spanish radio network linked to the Catholic Church's governing body in Spain, CNN reported Saturday.
The nuns were praying when Pope Francis called, so when no one answered, he left a message, the COPE radio network said.
Convent prioress Sister Adriana told COPE she "literally wanted to die" when she heard the message -- but she and her sisters were able to get the pope on the line eventually.
After consulting with a bishop, the nuns tried unsuccessfully to call Pope Francis, then waited, hoping he'd call back, CNN said. When the call came, they answered.
The pope spoke with the community's five nuns, three of whom are from his native Argentina, COPE said.
"The message from Pope Francis was to never lose hope, because sadness leads to spiritual sloth and hopelessness," Sister Adriana said.