I'm only walking the Camino next year and i too have an iPhone, so I have already downloaded VIBER and have been testing it around the world, it's free and you can talk for hours. All I have to do now is change my SIM card when I get to France.
This site is run by Ivar at in Santiago de Compostela.
This site participates in the Amazon Affiliate program, designed to provide a means for Ivar to earn fees by linking to Amazon