Using a Verizon iphone 5 in Taiwan
So I'm just back from Taiwan and have some experience using a Verizon iPhone 5.
The Verizon iPhone 5 is GSM unlocked. This means that if you have a nanoSIM card from a local provider (I had a prepaid card from Chung Wah) you can follow this procedure:
Turn off the phone, pop out the drawer using Apple's special tool, remove out Verizon's special card (retain for future use!), drop in your nanoSIM, reinstall the drawer, turn on the phone. This will probably even work in the US with a GSM provider like T-Mobile but I don't have actual experience.
To return to Verizon, reverse the procedure.
BTW, I tried to use my phone as a Verizon phone in Taiwan hoping that they would have some reciprocal arrangement with a local CDMA provider but, alas, no go. I guess there aren't any CDMA providers in Taiwan. This is unfortunate. I like to text my family upon landing just to tell them I've arrived. I can't on Verizon; have to go into the terminal where there's free wifi before I can email and I can't text internationally at all because my Taiwan prepaid plan doesn't seem to support it. Before, when I was with AT&T, texting worked even though I turned data roaming off.
One other downside at least for countries with no CDMA provider: if folks back in the old USofA want to reach you, they're going to have to call you on your local number, not your Verizon number. It'll be an international call for them. There was one time when I was still with AT&T that I was standing at the International Flower Expo in Taipei and the person who was house sitting for me happened to call. A very weird experience but seamless. Now with Verizon, that won't work.
iPhone 5, iOS 6.0.2