Bob wants to know where the best place to get a SIM card is for his Sprint iPhone when he's in Europe. Leo says that Sprint uses CDMA, not GSM, which is what's required for a SIM card. However, the iPhone 5 is a world phone, meaning it has both CDMA and GSM options. With Sprint, however, the GSM slot is locked. He could go to Sprint and explain to them that he's going to Europe and ask if they'll unlock it. Then he could buy a local SIM while he's in Europe. The chatroom says that if he's a customer in good standing, Sprint should unlock it.
He'll have to make sure that the SIM cards he buys are good in the countries he's traveling to. Check out this site for a list of SIMs in different areas. TruePhone should work, as will VodaPhone.
Dan F in the chatroom says to turn off the dataplan and use a MiFi instead.