lol what?
LTE roaming doesn't exist, and also I have a "global" 4S, but last time I checked the 4 works on EXACTLY the same networks in the same countries, and I just have my normal SIM in the side.
Im from the UK, we don't have ****** CDMA networks.
Well, no, you're wrong about the 4 and the 4S working on the exact same networks. The 4 is a GSM/UMTS phone that had a later CDMA model released. They're separate.
The iPhone 4S is GSM/UMTS/CDMA all on one radio. One phone model though the CDMA is, AFAIK, totally disabled in software for networks other than Verizon and Sprint. This is what Verizon and Sprint call a "global phone" (unlike Verizon's iPhone 4 which had CDMA only).
Verizon and Sprint CDMA global phones use a SIM card ONLY when roaming outside the United States. For Verizon, this is provided by their part-owner Vodafone. It is homed to either Vodafone UK or Vodafone NL and has a British or Dutch number that when online automatically tells Verizon's network in the US to forward incoming calls to it. It's a hack-job mess of global roaming. When at home in the US, the phone's MEID is used to authenticate it on the CDMA network.
With Verizon LTE phones, which use LTE for data and CDMA for voice (and data in non-LTE markets), Verizon uses a SIM card for ALL authentication. USIM application for LTE authentication, and CSIM application for CDMA authentication. This SIM card can be freely swapped between all Verizon LTE devices. I was telling the person that he was incorrect about the SIM not being used for CDMA *in Verizon LTE phones*
Now, my big question - why do the iPhone 4S (and other global roaming CDMA phones) not use the same SIM cards with USIM and CSIM? For that matter, why do they have no global roaming LTE phones (no Verizon LTE phones last I checked have GSM/UMTS)?
I don't know the technical reason (if any) for this, I only posted what I did to clarify that there's a HUGE difference between the SIM Verizon uses in CDMA global phones (a Vodafone SIM used only for international GSM/UMTS roaming) and the SIM Verizon uses in LTE phones (an actual Verizon SIM used for all authentication including CDMA vis CSIM).
1. Perhaps the reason is marketing (SIM swapping is a cool new LTE feature...).
2. Perhaps the reason is roaming agreements (i.e. Verizon may not want to negotiate a full set of International roaming agreements, instead preferring to rely as they do now on the global roaming agreements of their 45% parent Vodafone).
3. Perhaps there are unresolved technical switching considerations required in bringing roaming voice traffic from the GSM MAP core into Verizon's legacy ANSI-41 MAP. Here is a white paper from 3GPP2 (the people officially behind CDMA, basically a front for Qualcomm) on how this can be accomplished though:
http://www.3gpp2.org/public_html/specs/N.S0028-0_v1.0.pdf
I'm inclined to believe it's a mix of 2 and 3. That not only would they have to negotiate roaming agreements all over the world (instead of using Vodafone's), they'd have to work with these carriers to help implement GSM/ANSI-41 interoperability. While obviously, due to their part ownership, it should be no problem getting Vodafone to do this, other international carriers - especially in smaller countries may be more reluctant.
These issues may need to be resolved, at least domestically anyway, before Verizon can start the migration to VoLTE, which will use Diameter, the replacement and official migration path from the GSM MAP. Where are the LTE global phones? Perhaps we won't see any until VoLTE is implemented and Verizon is using Diameter all around, including for voice traffic. What will happen when these subscribers leave the Verizon LTE coverage area? While Verizon will have the vast majority, if not all, of their native coverage overlaid with LTE before they deploy VoLTE on any wide scale. But what happens when these customers go to say, Alaska, where Verizon has no service? Today they roam on a local CDMA network. Will Verizon VoLTE phones support CDMA and have ANSI-41 interoperability working? Will Verizon VoLTE phones be GSM/UMTS/LTE devices and roam on arch-rival AT&T in those areas? What about global phones? If Verizon's main switching for VoLTE is Diameter and they use ANSI-41 interoperability to roam domestically in areas without Verizon LTE coverage, then foreign carriers would have no potential ANSI-41 compatibility issues. I could see VoLTE bringing a substantial loss of coverage to Verizon customers if they don't implement ANSI-41 interoperability with rural CDMA carriers and they don't allow GSM/UMTS roaming on arch-rival AT&T. Perhaps that's the point behind Verizon's LTE in Rural America program?
It will be interesting to see how this all plays out.
As for LTE roaming, sure it exists. Not deployed yet, but the capability is there. But at approx US$2-10/MB in data roaming charges (depending where you are in the world and who your home network is) and the insane number of bands LTE is getting shoehorned into, who wants it yet?
UPDATE - I corrected myself. LTE does not use the GSM MAP (aka SS7/MAP) as we know it. It uses a new protocol called Diameter which is the intended replacement for the GSM MAP.
UPDATE 2 - The necessary integration, whatever it may be, might be coming soon. Further research shows that both the Motorola Droid 4 and LG Spectrum have radio chipsets with support for GSM/UMTS; and early leaked inside information stated they'd be global roaming phones. While it's possible this means nothing (both the iPhone 4 and 4S have radio chipsets supporting UMTS-1700 for example...), there is a possibility (if other needed hardware is in place) that a future firmware upgrade could enable this ability and an unnamed "Verizon representative" apparently states it will. Take with a huge grain of salt:
http://pocketnow.com/android/verizon-confirms-global-roaming-for-new-lte-smartphones
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