I am only charged if I answer and talk. If it goes to voice mail, no charge.

My daughter was not charged a fee, as far as she is concerned, she's just calling my regular US number.

Edited to add:
It works this way all over the world and on Royal Caribbean, Celebrity, and Azamara (before they were sold) cruise ships but sometimes the fees are different.... well, at least where I've tried.... Tahiti, Spain, Portugal, and several spots throughout the Caribbean.