How can I use a Verizon iPhone 4S overseas with a local SIM?

Michele's daughter is going overseas and she has an iPhone 4S. How can she use a local SIM while she's there? Leo suggests upgrading to the iPhone 5, 5C or 5S through Verizon. It's a world phone and she can then use a local SIM when she gets to where she's going. Asking Verizon to unlock the 4S may not work because it wasn't a GSM phone. And that iPhone 4S wouldn't work where she's going anyway. So upgrade and then you can do what you want.