Network Hopping Won't Work Without an Unlocked iPhone 4S

By Wesley Fenlon

While iPhone 4S handsets activated on Sprint, Verizon and AT&T will be able to roam internationally, only unlocked iPhones are guaranteed to be able to use foreign GSM SIM cards.

Worldphones promise we can swap out SIMs or hop onto foreign CDMA networks in any country in the world without spending exorbitant amounts of money on roaming charges. It's the dream for frequent travelers: nothing beats a phone that works on both CDMA and GSM networks. Unfortunately, that's a dream globe trotters won't be able to realize with a $200 iPhone 4S.

Though Apple's next phone contains GSM and CDMA radios, the model you purchase will determine which you can use, and GSM-locked phones won't have CDMA access at all. Only the full price unlocked iPhone 4S will be guaranteed to work with foreign SIM cards--and it won't work on CDMA networks, either.

There are three different ways to go when buying an iPhone 4S: GSM via an AT&T contract, CDMA via a Verizon/Sprint contract, and contract-free with a full price, unlocked phone. If you opt for GSM, the CDMA radio will be disabled according to Apple's iPhone comparison:

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

If you buy a CDMA phone via Verizon or Sprint, you actually will be able to use GSM technology. But only roaming, not through foreign SIMs, according to the Apple FAQ:

If you choose AT&T as your wireless carrier, your iPhone 4 or iPhone 4S will use only GSM cellular technology for voice and data services, and it can roam internationally on 200 GSM carriers around the world. If you choose Sprint or Verizon Wireless as your wireless carrier, your iPhone 4 will use only CDMA cellular technology for voice and data services. An iPhone 4S activated on Sprint or Verizon Wireless will use CDMA technology too, but it also has the ability to roam internationally on GSM networks using the provided GSM micro-SIM.
... iPhone 4 for Sprint will work in approximately 35 countries and iPhone 4 for Verizon Wireless will work in approximately 40 countries that use CDMA technology.

So you can use your Sprint/Verizon phone in CDMA countries, but you'll have to deal with carrier roaming charges to talk internationally and might have to pay extra on your plan to even have that option. And then there's the third course: buying an unlocked iPhone for $650 or more. It will not work with CDMA:

The unlocked iPhone includes all the features of iPhone but without a contract commitment. You can activate and use it on the supported GSM wireless network of your choice, such as AT&T in the United States.* The unlocked iPhone 4 or iPhone 4S will not work with CDMA-based carriers such as Verizon Wireless or Sprint.
If you don’t want a multiyear service contract or if you prefer to use a local carrier when traveling abroad, the unlocked iPhone is the best choice. It arrives without a micro-SIM card, so you’ll need an active micro-SIM card from any supported GSM carrier worldwide.

The unlocked iPhone 4S doesn't start shipping until November. There's actually a fourth option we haven't listed yet: jailbreaking your phone and unlocking the ability to use a SIM abroad. We can only assume that will be an option once hackers get their hands on the new phone--just don't bet $200 on that fact, if affordable overseas calling matters to you.

Image via flickr user qiaomeng