AT&T --> Sprint, and other GSM-CDMA confusions

1. iPhone 5c and 5s models support both GSM and CDMA, so they could be moved to other networks. There was an iPhone 5 model that also supported both protocols.
2. The new upgrade program requires that you sign-up with one provider. You cannot switch providers day after day. In order to change a provider the one you have must first unlock your device. That is at the provider's option. You can take the 6s to Mexico if you can find a provider that supports it and if your current provider will unlock it.
3. This depends on the provider. Sprint and AT&T have different networks. The phone must support both and the provider must be willing and/or able to unlock the phone.

Idaho Redneck wrote:

1. I have iPhones ranging from 3G - 5s. They were all purchased from AT&T, but are out of contract and so can be unlocked. Can these phones be ported to Sprint or to any CDMA network?

2. If I buy a new iPhone 6s directly from Apple with the new upgrade program, can I use it with AT&T one day, Sprint the next, and Verizon the next? Can I take it to Mexico, pop a local sim card into it, and use it as a Mexican phone?

3. If I lease a phone from Sprint and pay it off, can I sell it to an AT&T user?

It's hard to do your own research with so many conflicting success and failure stories, and mixed up theories. Please help.

1. No. Though the 4S, 5, 5s and 5c are technically capable of it, the CDMA carriers will not activate any device that is not in their database. This is changing. However... Verizon will activate non-Verizon iPhones on their network, but only the iPhone 6 and higher.

2. Yes and no. Activation on a CDMA carrier is more than just a matter of inserting a SIM. Unless the device is activated by the carrier, it will not work on the CDMA network. It would work on a CDMA carriers LTE network, but not on their CDMA network. If you were to wander out of range of the LTE signal, you would have no service at all. A device can also not be activated on more than one CDMA network at a time. You're either on Sprint or Verizon, not both, and switching from one to another is a PITA. Sprint has not announced any plans to accept non Sprint phones on their network.

3. So long as Sprint is willing to unlock it before you attempt to sell it, yes. Getting phones unlocked by Sprint for use on US GSM carriers is also a PITA, and not always possible at all.

If American carriers decide to play nice, which may be a long time coming you eventually could do something like this:

You can do CDMA to GSM meaning you could take an unlocked Verizon/Sprint phone to At&t/T-mobile/International

You can't go from GSM to CDMA unless the phone is known to have both radios in it (See previous post about bringing unlocked phones to Verizon)

Actually on #2, with the upgrade program, the phone is unlocked. CDMA versions will only Roam on GSM networks in the US, however.