Bob is going to be traveling overseas and he'll be using his iPhone 5 while he's there. Leo says it can be done, but he should turn data roaming off. That means he won't have any data while he's out and about, though. But it also means he won't have a phone bill in the thousands.
If he wants to be able to use data, he can get an international data roaming plan. He can download apps that offer cached maps. Leo uses Motion X GPS Drive. Google Maps will work offline too. He can just select the area he wants, and then download the data.
Another option is getting a local SIM when he gets to his destination. His phone will need to be unlocked for that. He can check out PrepaidWithData.Wikia.com for more on this.