A few things:

Get a Capital One Visa because they do not charge a 3% foreign exchange fee. Many others do. If not Capital One, get one with a RFID chip. They are easier to use in Europe. Capital One still doesn't make an RFID card.

ATMs work great for local currency.

AT&T will unlock the iPhone for free now (using an iTunes sync) if you call them and set it up first. You must be out of contract and paid up. Then in zeurope you can replace the ATT sim card with a local much cheaper sim card.