In-Depth: Why iPhone 4S Can’t use CDMA on GSM Networks

I’ve posted a few brief comments on Steve’s passing on my personal blog…

It’s not 100% clear yet if all iPhone 4S variants will have CDMA hardware inside, but Apple has made one thing clear; if you purchase an iPhone 4S from AT&T, a GSM/UMTS carrier, or an unlocked version, you won’t be able to use it on CDMA carriers like Sprint and Verizon.

Many sites, including a few of our competitors, were unsure why Apple made this move. Thankfully, we have the answers.

Presuming all iPhone 4S variants have the necessary CDMA hardware, we explore the history, and answer why, you cannot activate that CDMA radio on a GSM carrier. And, we’ll also tackle the difficult questions for CDMA customers of roaming on GSM that iPhone 4S has raised.

And yes, there’s a history lesson involved.

First, a primer. CDMA is the abbreviation for Code Division Multiple Access, and its more modern version, CDMA2000, which is the network that Sprint, Verizon, MetroPCS, Leap/Cricket, and others use today as their primary network. GSM/UMTS are the (2G/3G, respectively) networks that T-Mobile and AT&T use.

GSM/UMTS is primarily used in Europe and much of Asia. CDMA is the predominant network in the Americas, and portions of Europe. While CDMA does not have a technical future, its diminishing cost has driven it to developing nations, while GSM/UMTS are migrating to the newer LTE technology. As such, Sprint and Verizon will also eventually be using LTE as their primary networks.

Up until now, there have been practically zero phones that operated on both CDMA, and GSM/UMTS, in the same country. There are a plethora of international devices however that operate on the frequencies used abroad, as well as networks locally. Even when devices supported both CDMA 3G and GSM 2G, they rarely have supported the U.S. GSM, UMTS, and CDMA frequencies at once.

Much of this has been at the behest of US carriers. Regulatory concerns crop up once CDMA and GSM carriers can interact with one-another. Specifically, each and every carrier fears that the FCC may begin to mandate that the carriers act homogeneously. If the carriers can claim technical barriers to that, then they can stave off FCC mandates regarding roaming, interoperability, unlocking of devices, stolen device databases, and well, we’ll end the run-on sentence there.

This makes iPhone 4S a bit of a game changer. Technologically, there’s nothing stopping a Sprint or Verizon customer from accessing AT&T’s “4G” GSM/UMTS/HSPA+ network. They could also theoretically access T-Mobile’s 2G GSM network.

However, they can’t. The reason is aforementioned paragraph regarding why the carriers have not wanted this innovation; they don’t want all the carriers being interoperable, as it opens the door to regulation. As such, none of the roaming agreements are in-place to allow for Sprint and Verizon customers to fall back to GSM/UMTS/HSPA, nor is there a roaming agreement for AT&T or T-Mobile customers to hop on Sprint and Verizon.

Now we start to see how this situation came about. Of course, if your iPhone is locked to AT&T, activating on Sprint or Verizon is not going to happen, so Apple simply disabled CDMA at the firmware level.

GSM carriers have abhorred the more-robust CDMA2000, some in Europe even made it illegal to deploy such a network in many areas through regulation and “discretionary mandates”. As such, international roaming in places like Brazil, Mexico, and elsewhere, cannot happen on the GSM side of things.

Apple, out of care to the carriers that are their largest customers, simply is disabling the CDMA portion of the device when initially activated on a GSM/UMTS carrier. This prevents all of these questions, and calls for comprehensive roaming agreements to occur.

It also prevents people from scamming AT&T out of a $400 subsidy, and then running the device right over to MetroPCS or Cricket.

The next question that then comes to mind is why you cannot take a device from Sprint to Verizon, and vice-versa. CDMA, unlike GSM, does not have firm subsidy locks, instead using an antiquated Master Subsidy Lock code system. As such, the risk of people ripping off a carrier is high. Customers have already hijacked “frozen” Verizon iPhone 4 devices and activated them on MetroPCS and other regional carriers, in areas where the devices are compatible (part of MetroPCS’s coverage uses the 1700 MHz frequency, which iPhone does not support currently on CDMA bands).

As such, Apple is again helping the carriers. While Apple cannot (totally) stop jailbreaking, they can ensure that unlocked versions of iPhone 4S are limited to the carriers that have openly accepted unlocked devices with open arms (AT&T, T-Mobile, and the MVNOs that operate on those networks).

Sprint has agreed, years ago, in a settlement to unlock devices, but with proprietary carrier configuration settings, this is of little benefit. You cannot change the inaccessible settings to make the device work properly on other CDMA networks. Verizon claims to accept unlocked CDMA devices through a similar settlement, but only accepts a list of antiquated devices that can be hacked with a common tool — and will not activate a Sprint iPhone 4S, even if the subsidy has been fully paid.

In sum, most of the rules of CDMA vs GSM that Apple has laid out are of their own making, designed to appease the carriers that flagship their devices. The rules are born out of a history of antiquated technological boundaries that are no longer valid. It will be left to consumers to demand that things change.

This article was revised after initial posting, to clarify Sprint and Verizon’s positions on CDMA device unlocking and importation.