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I'd like to know if I could factory restore my iPhone 4S, insert a SIM card and see if that would make it activated in the other GSM network. The phone was bought from a regional CDMA carrier but they're being extremely shady in confirming whether or not it's SIM locked and if they'd be willing to unlock it for me.

I bought it out of contract and took their service on a month by month basis but it's becoming extremely expensive. Are there any options of unlocking my iPhone 4S (CDMA) to use on a GSM network? And if not, why?

You can see here what iTunes told me after I had reset the phone to troubleshoot a issue and suddenly got the idea but didn't try it because I didn't have a micro-SIM card at the time.

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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.

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No, if you purchased an iPhone 4S that utilizes CDMA, you will not be able to coerce it to function with GSM technology.

As per the iPhone 4S Technical Specifications page:

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

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  • If GSM phones won't work on CDMA, that doesn't necessarily mean that CDMA phones won't work on GSM. On the iPhone 4s tech specs page there's clearly a warning not to expect CDMA service from devices sold into GSM service, but no warning of the opposite. I would only agree with your "not able to coerce it" if you stipulated that the GSM carrier was in direct competition for customers as the sold-in-to-CDMA carrier. Clearly many iPhone 4s work fine with GSM technology as long as the SIM slot is unlocked.
    – bmike ♦
    Nov 7 '13 at 13:53
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Let me disagree with this answer. Actually, you can use a CDMA iPhone 4S and iPhone 5 with a GSM network once it's factory unlocked. The catch is that Sprint and Verizon network's can not be used with any GSM network in USA. It is unlocked only for international GSM networks. Yes, CDMA iPhone 4 can not be used with any GSM network.

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  • The 4S/5 models are both GSM and CDMA, the 4 has two different models
    – nohillside ♦
    Aug 26 '13 at 13:36
  • I agree with Amit's basic assessment and have linked to what I see as the relevant specs in my answer below. Also - @patrick may be correct that the hardware is identical, but clearly Apple is marketing and even printing different back plate model numbers for the CDMA iPhone 4s than it is for the GSM 4s.
    – bmike ♦
    Nov 7 '13 at 14:05

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