I wonder if the unlocked iPhone 4S would be able to accept CDMA SIM cards? The newest version of the CDMA2000 1XEV-DO standards include support for removable user identity modules.
These days, the user identity program is stored on standard UICCs, which can have CSIM (CDMA) and USIM (GSM/UMTS/LTE) programs installed on the same module. This is quite common in India where carriers have to roam with everybody to get enough coverage of the nation, so most feature phones in India are dual-mode (though most people don't notice it).
In Asia, the newer CDMA standard that requires SIM cards is used. For example, mobile operator au by KDDI in Japan uses SIM cards for their phones even though au is a CDMA2000 operator. In fact, their service runs on 850MHz (though it is mistakenly called CDMA 800), which is supported by the iPhone 4S because Verizon uses that frequency band too. They are also getting the iPhone 4S along with UMTS operator SoftBank Mobile.
The reason why I'm hoping the unlocked iPhone 4S can support CDMA SIM cards is because they are starting to become available in America too. MetroPCS was the first carrier to offer it, and Verizon Wireless did it shortly afterward. Going forward, U.S. Cellular, C Spire Wireless, and Sprint all plan to deploy CDMA SIMs as part of their migration to LTE. LightSquared will be deploying SIM cards that support CDMA, GSM, WCDMA, and LTE operation, since one of the conditions for becoming a LightSquared partner is reciprocal roaming for LightSquared customers and carriers that sign up for LightSquared LTE service. Clearwire (if they ever get money), will be deploying LTE-only SIMs, probably.
While LTE operators are using incompatible bands, all the CDMA networks in the United States (with the notable exceptions of MetroPCS and Cricket) are fully band frequency compatible. MetroPCS and Cricket both use CDMA on AWS (1700/2100) and PCS (1900). So the iPhone 4S only works on one of the frequency bands. That being said, people on those two carriers roam A LOT on Sprint or Verizon, so it may not matter.
These days, the user identity program is stored on standard UICCs, which can have CSIM (CDMA) and USIM (GSM/UMTS/LTE) programs installed on the same module. This is quite common in India where carriers have to roam with everybody to get enough coverage of the nation, so most feature phones in India are dual-mode (though most people don't notice it).
In Asia, the newer CDMA standard that requires SIM cards is used. For example, mobile operator au by KDDI in Japan uses SIM cards for their phones even though au is a CDMA2000 operator. In fact, their service runs on 850MHz (though it is mistakenly called CDMA 800), which is supported by the iPhone 4S because Verizon uses that frequency band too. They are also getting the iPhone 4S along with UMTS operator SoftBank Mobile.
The reason why I'm hoping the unlocked iPhone 4S can support CDMA SIM cards is because they are starting to become available in America too. MetroPCS was the first carrier to offer it, and Verizon Wireless did it shortly afterward. Going forward, U.S. Cellular, C Spire Wireless, and Sprint all plan to deploy CDMA SIMs as part of their migration to LTE. LightSquared will be deploying SIM cards that support CDMA, GSM, WCDMA, and LTE operation, since one of the conditions for becoming a LightSquared partner is reciprocal roaming for LightSquared customers and carriers that sign up for LightSquared LTE service. Clearwire (if they ever get money), will be deploying LTE-only SIMs, probably.
While LTE operators are using incompatible bands, all the CDMA networks in the United States (with the notable exceptions of MetroPCS and Cricket) are fully band frequency compatible. MetroPCS and Cricket both use CDMA on AWS (1700/2100) and PCS (1900). So the iPhone 4S only works on one of the frequency bands. That being said, people on those two carriers roam A LOT on Sprint or Verizon, so it may not matter.
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