The only reason I mention it is cost. Depending on their iphone and plan fees, sometimes Google voice or even Skype can be a lot cheaper for the occasional overseas call. Google voice and hangouts offer some pretty cheap alternatives but for wifi only calling. Just depends entirely on how much overseas calling the OP intends to make, and the fees for whatever plan they have, or intend to use with the iPhone. And if they have something like Skype and only plan on calling other Skype users.
The cost/fee structure (options matrix?) can get complicated (but option rich) depending on what you have, and who you’re calling.