I had a similiar question and wrote to Verizon through their webpage.
The answer I got us this...
All of our 4G LTE devices are not SIM locked and can use a foreign SIM. The device can use other GSM networks, however, we cannot guarantee that the carrier you want to use it on, will be able to provide service for it. Our 3G GSM enabled devices are SIM locked, but can be unlocked by us. The iPad 4G and the iPhone 5 do not require anything to use an alternative SIM, and can be activated with that foreign SIM + iTunes. If you'd like to discuss global options through Verizon Wireless, please call us at 800-711-8300.
Hope this helps
I asked the question to verizon customer service and this is the reply I got..
I am happy to know that you are excited about the new iPhone 5 and that you have already pre-ordered these phones for you and your wife!! I just know that you will absolutely love your new phones. Of course, I will be more than happy to review the iPhone 5s features and share if the phone will have an unlocked SIM card. I know that this is important for you when you travel abroad to India. Please accept my apology for the delayed response to your email. My name is Adrian and I will be your account advocate today.
I looked over the features for the iPhone 5 and I was unable to confirm that this phone has an unlocked SIM card. I know that this may have come as a great disappointment to you as you are aware that using service in India right now is costly and requires altering of your phone. I truly apologize for any inconvenience this matter may have caused.
Although I was unable to give you good new, I hope the details that I have shared with you is helpful. I appreciate your business and thank you for being a VZW customer. Have a wonderful day!!
I still find it unbelievable that people insist on posting to a blog stating the untrue and mis-informing people looking for answers on here. I do appreciate the fact that people are trying to help others but if the correct answers are not posted, it does nothing but upset people. The Verizon iPhone does indeed come unlocked.
Verizon iPhone 5's secret feature: It's 'unlocked !
09/22/2012 5:58 AM ET
The Verizon Wireless version of the iPhone 5, which went on sale Friday, comes with a secret and unexpected feature: it works on AT&T's network as well.
Confirming blog reports, The Associated Press found that the Verizon iPhone 5 accepts an AT&T "SIM card" _ a little chip that identifies a phone to a wireless network. The phone can then be active on AT&T's network.
It's the first time Verizon iPhones have been able to access AT&T's network without complicated hacking procedures. The feature may mean little to most buyers, since they're signing up for two years of Verizon service. But it does give them the option of switching carriers.
It's unclear whether the feature is intended and whether the phones will work with other carriers, such as T-Mobile USA. But Verizon Wireless spokeswoman Brenda Raney confirmed Saturday that the iPhone 5 models it's selling are "unlocked."
Last year, the first shipments of the Sprint iPhone 4S were unlocked and worked on AT&T, but Sprint later issued software updates that turned off that capability.
I got a similar reply from Verizon. This response contradicts the other reports. Is she wrong? I mostly care about having the most carrier flexibility within the USA, several European countries, and China.
<b>Thank you for inquiring with us about the new iPhone 5. My name is Rachael and I am happy to help today.
The iPhone 5 is not a phone that can be unlocked, nor do we sell an unlocked version of the phone. It is able to be activated on the Verizon Wireless network, but is not yet global capable. I apologize for any incorrect information that you may have received.
If you have any questions or concerns, please don't hesitate to let us know! Thank you so much for contacting Verizon Wireless, and I hope that you have a great rest of your day!
Ok Guys. Lets settle this once and for all.
Verizon comes with an unlocked GSM slot. Verizon confirmed this to Associated Press. See link below.
Hope this puts an end to this discussion.
Based off of my research- Yes. If you use a SIM card (i.e. while you're in the UK)- there's an option to turn off CDMA while roaming (from some reports, i've heard that when it senses a foreign sim it'll turn off CDMA automatically).
So for your purposes, I believe the VZW one is the best bet.
The only downside i can see however, is if you come to the states and want to sign up on ATT- you won't get ATT LTE network speeds (but would get 3G), but obviously you'll be able to use ATT GSM network since VZW is unlocked. Also- if you want to change to sprint- i don't believe that is possible.
I'm in multiple continents for months at a time throughout the year, so for me i think the VZW iphone 5 is the best. It has all the same bands covered that the unlocked one in Asia supports, plus an a few add'l LTE bands, and CDMA. CDMA i won't actually use- but it's nice to know it's there.
As far as data/voice dual usage- i don't believe it'll be a problem when you're on GSM networks- the limiting factor is the CDMA network/chip- since that'll be disabled while you're on GSM, you should be fine (but again, this is just a theory).
I'm using VZW- which i use with Tmo in the states (i get 3G in parts of manhattan), Three in HK (should be LTE- i'll find out in a few days) and Voda in UK (again LTE- but won't know for a few wks)