Is is possible to move a Verizon iPhone 4s to another US cellular carrier? Is it possible to use a Verizon iPhone 4S on another US carrier, such as GSM AT&amp;T or T-mobile or CDMA Sprint, etc? And why if not?

Assuming the devices has been legitimately unlocked via the procedures mentioned in  Verizon iPhone 4S SIM UNLOCK Tutorial?


  Verizon has confirmed (here and here) they WILL unlock the SIM on the iPhone 4S, allowing for use of local SIM cards while traveling abroad (no word yet on whether this will allow for use on AT&amp;T and T-Mobile.) This is different than the jailbreak unlocking method; SIM unlocking through Verizon is permanent and will not affect your warranty in any way.
  
  
  Meet the following requirements:
  
  
  Must be a Verizon Wireless customer.
  The iPhone 4S being unlocked must be active on a Verizon Wireless line of service.
  The line of service must be active at least 60 days.
  The line of service must be in good standing for the past 60 days.
  Only one SIM Unlock per line every 10 months.
  
  
  
  If you don't meet one or more of the above requirements, call anyway. You may still get lucky.
  
  
  Insert a foreign SIM into the SIM card slot on the side of your phone (only required to confirm that the unlock is successful.)
  Call 1-800-711-8300 (Verizon Global Support) and ask the representative for a SIM unlock. Occassionally a representative may not know exactly what you are referring to; make sure you are not transferred to a different department. You are in the right place. Explain that they should have a walkthrough on how to do this, and that it allows for the use of local, non-Verizon SIM cards while traveling abroad.
  Get confirmation from the rep that the unlock has been applied to your account, then check your phone to make sure it recognizes your SIM and can connect (if successful it will roam on AT&amp;T, assuming you are calling from the USA.) You will NOT see an unlock confirmation in iTunes as that is for a factory-applied unlock only.
  Enjoy your new unlocked iPhone 4S!
  


However it seems that this unlock mentioned above is only for Internationale SIM cards for use outside of the US. Can this be done in the US, really looking for other carrier options with my existing phone.
I think I found the Answer I was looking for in How U.S. Carriers Fool You Into Thinking Your iPhone 4S Is Unlocked
Short answer &quot;You can't do it!&quot; If your phone is CDMA, its permanently locked to its CDMA network of origin.

Unlocking your Iphone 4S
Among the three major carriers operating in the U.S., only one, AT&amp;T, will not unlock any iPhone. Because I purchased a Verizon-designated handset, the following information relates to those customers that purchase Verizon iPhones, but the technology and result is the same for any carrier.
When I called Verizon tech support to unlock my phone prior to leaving the U.S., I was told that I had to have a foreign SIM card installed in order to complete the process and that the phone would have to log in to the Verizon network on WiFi. The reason for this procedure is that the phone must validate the foreign SIM.

...

So I stopped in at an Apple store in London. We logged into a WiFi network, installed a micro-SIM card from a carrier in England, and within about thirty seconds, the phone was unlocked because Verizon had already unlocked the phone at their end before I left the U.S. For the rest of my travels overseas, it worked flawlessly and provided essentially the same options that are available on any other dual-mode or GSM-only device.

...

Four different iPhone 4S versions
When I returned to the U.S., I wanted to confirm that my Verizon iPhone could be ported to another carrier, whether CDMA or GSM. This was the intent of Apple when they designed the 4S: every phone is the same and will work on virtually any carrier in the world.
So, I contacted a regional GSM carrier in the Midwest that has roaming agreements with AT&amp;T and T-Mobile. The carrier was kind enough to provide a micro-SIM card for testing in my iPhone. What I found may infuriate customers who have purchased expensive iPhones from one of the three carriers in the U.S. but at some point decide to switch to another provider because of poor coverage, customer service, or pricing.

...

Sitting in South Dakota, I replaced my Verizon SIM with the Longlines Wireless chip. The phone indicated that the SIM was not recognized by the phone and required its removal and device reboot. I contacted Verizon global support to confirm my suspicions. They advised that indeed their phones were locked as against any other carrier in the United States, and that the term “unlock” only applied to overseas carriers.
I next inserted my UK SIM card into the phone, and it logged into AT&amp;T without issue, which confirmed what Verizon told me. I then interviewed managers at three different Apple corporate stores to confirm issues with regard to unlocking.
What consumers need to understand is that there are actually four different versions of the iPhone 4S: Verizon, Sprint, AT&amp;T, and Apple. Only the Apple phone, available from their stores or on-line, is fully unlocked and can be used on any carrier outside the United States. The other phones are permanently locked and cannot ever be used on another carrier in the U.S. Even if you spend $800 for an unlocked phone as I did and dedicate it to a single U.S. carrier, you are locked into that carrier forever if you want to keep using the iPhone. Neither Apple or the other carriers will fully unlock your carrier phone.