International phone cards?

My niece needs a phone card that will enable her to call home from her “semester@sea” cruise ship. The cruise includes Salvador, Brazil, Rio de Janiero, Capetown S.A., Chennai, India, Ho Chi Minh City, Viet Nam, Malaysia, Hong Kong, Japan, Hawaii, Costa Rica….. How do phone calls work from a cruise ship? Would it be better to just call from the land stops? What card gives the most minutes per dollar? And can be used from all of these international sites?