Bob's wife is traveling to Italy on vacation and wants to know if she should bring her iPhone. Leo says that she could pay for an international data roaming plan. They're not cheap and the data caps are small, not to mention the cell call charges.
Another way is to turn off data roaming. She won't have data unless she has Wi-Fi access, like at her hotel. Some apps, like Google Maps, would allow her to cache data while away from Wi-Fi.
The third option is to have her carrier unlock her phone. They will likely do it if her account is in good standing. Then she could get a local SIM that she could put in her phone while she's there. The advantage of that is that she'll have a local number. The good news is that Bob's wife has an iPhone 5 which is a world phone and is unlocked. So she's good to go on that option. Leo advises going to this site for pay as you go Sim information in Europe.