IPhone – Is it possible to use a Verizon CDMA iPhone 4 with any other carrier or Pay-Per-Use carrier

The answer to this question is slightly complicated and in essence becomes: it depends which CDMA carrier device you purchased and which GSM carrier you want to switch to.

First the facts - there are three "models" of iPhone 4s sold according to the model number on the back cover:

• A1431: iPhone 4s (GSM model China)
• A1387: iPhone 4s (CDMA model)
• A1387: iPhone 4s (GSM model)

People wanting to use models A1431 and A1387 on CDMA networks are basically out of luck as there seems to be no support from Apple to reprogram the device to even work on CDMA. I don't know if it's a hardware issue or just drivers/software, but it's clearly stated in the Technical Specifications as footnote 3:

3. CDMA available only if iPhone 4S is sold and activated for use on a CDMA network.

There is no indication that GSM is not available on CDMA phones, however my experience is that CDMA carriers Verizon and Sprint won't unlock the GSM sim slot until between 30 and 90 days after you have initiated service on that line.

Additionally, I have heard reports that the unlock is smart enough to prevent a GSM carrier that competes with the CDMA carrier from taking over service of the device. So, in the USA - a Sprint or Verizon phone would not be expected to work with AT&T or T-Mobile USA cards, but would be expected to work with any European, Asian, or other non-US based GSM carrier. I do know of many people that have travelled internationally with Sprint or Verizon iPhone 4S and had no problem once they unlocked, but I've not heard that any GSM card works - either while the phone is under contract with the original CDMA carrier or after that contract period expires.

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 "You can't do it!" 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&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&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&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&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.