Invest in an Unlocked Cell Phone
Cell phone rates abroad are outrageous. The Independent Traveler put together a nice read analyzing the pros and cons of purchasing your carriers international plan. Either way, you could be paying upwards of $1.00/minute of international calling, and that can add up.
I suggest investing in an unlocked cell phone. This means that your cellular device has no restrictions and allows the user to pop in and out sim cards from wherever they are. Purchasing sim cards will lower your cost because they allow you to only purchase the minutes you need. Large carriers typically sell international plans, and if you end up not using all your minutes, then you are just wasting money.
Be sure that when you purchase your new international phone that it is 100% unlocked. As of right now, if I were to insert an international sim card into my iPhone 6+, it would not work because the manufacturer has placed a lock on it. This is something they do to ensure you purchase their plans and increase their revenue.