There isn't an unlimited plan but there is a Global Data plan. It is $25 for every 100mb od international data used. It is set up in a way that when you exceed the 100mbs it automatically gives you another 100mbs for another $25. Call customer service to have them check your eligibility and add this for you.
Turkey sounds like a fantastic trip right about now. And we'll be sure to make sure you're taken care of while abroad. Now, as advised by a fellow community poster, there is no unlimited international plan you can add but you should check out our international trip planner so you can view your options and add them via My Verizon http://vz.to/n9PFe9 .