4G LTE SIM swap?

March 12, 2012 11:39 AM

Please enlighten me about Verizon LTE SIM cards.

I have a Verizon Galaxy Nexus, and it's my first phone that has ever had a removable SIM card. I really don't understand how SIM cards work, so please pardon my ignorance.

Verizon has a separate data plan you need for, say, a 4G tablet or a 4G USB dongle.
But I've been grandfathered in to unlimited data on my phone.

So.. what would happen if I took my SIM card out of my Galaxy Nexus and inserted it into a 4G ipad3, for example?

Would I be able to use my unlimited data plan in the ipad?
Would my phone still work at all without the SIM card in it?
Is this a violation of any terms of service?

(Answers about other types of SIMs are OK, but I really want to know if anyone can specifically answer the question about Verizon ones before I end up blowing up both my phone and a tablet)

posted by jozxyqk to Computers & Internet (6 answers total)

Best answer: The SIM contains a serial number, some arbitrary data files, and a cryptographic engine which can respond to password challenges. Ultra-simplified version: the network says "hey, you claim to be serial number X, so take this timestamp, run it through your crypto engine with your secret key, and tell me the response. I have your secret key in my database, so I can check your work." If the SIM really has the secret key, the response will match what the network expects and he then trusts your phone.

All SIMs "speak" the same language to whatever is connected to them. It's a serial protocol with well-defined levels, baud rates, and messaging. So you won't blow up a device by trying a SIM in it. You might brick the SIM if the device misbehaves and sends it commands that make the SIM think you're trying to crack it, but that's rare.

So in theory, yes, but in practice, not as well as you'd hope. SIMs on Verizon's network are a slightly odd beast, because their network is currently a hybrid of non-SIM-based CDMA (3G, 3.5G, whatever you want to call it) network and SIM-based GSM-style (LTE, 4G, etc.) network. Verizon "4G" phones (note: LTE R9 is not actually 4G... you have to go to LTE Advanced to legitimately call it that, but marketing people don't listen) actually have two radio subsystems in them: one CDMA/1x/EvDO at 800 and 1900 MHz and another LTE at 700 MHz.

So in theory any device which can is built to talk LTE at 700 MHz will take your SIM and work on the parts of the Verizon network that have been upgraded LTE. Since AT&T has announced their LTE network will be down at 700 MHz, too, you might even be able to put your Verizon SIM in an AT&T LTE device and have it work. In theory, yes, but there are a lot of places where that assumption can go wrong.

If the device is a Verizon device (or a kissing cousin of something supported on Verizon's network) then the non-LTE parts of the network might even work, too. It's been a while since I tried, but getting that part to work was a crap-shoot. I imagine things get better as time moves forward.

(This whole problem is considerably easier when in pure GSM-style networks like AT&T, T-Mobile, Europe, etc. There, a SIM is a SIM is a SIM. The only place you have trouble is things like T-Mobile's "high speed" network is on a funky frequency here in the U.S. due to them losing out in the spectrum auction. So while your T-Mobile SIM will work in an AT&T phone no problem, you might not get 3G data unless that AT&T phone was built with hardware to support the extra T-Mobile funky band.)
posted by introp at 12:20 PM on March 12, 2012 [2 favorites]

Response by poster: It would all be between Verizon devices.
But, from what you're saying, I guess my phone would cease to work with anything other than wifi -- that is, not send or receive calls at all, never mind data -- while the SIM card was out? I can live with that; I'm just curious.
posted by jozxyqk at 12:51 PM on March 12, 2012

That would be a reasonable guess, though I don't actually know how much of the CDMA part of the phone (the A-key, PRI, etc.) got moved into the SIM. Maybe none, in which case your phone would continue to work as a 2G+3G phone. Maybe all, in which case your phone would act like it had no service and only allow emergency (911) calls. Maybe some combination of the two! Sadly in this case, the job where I wrote lots of code for such phones is in my recent past now.
posted by introp at 2:42 PM on March 12, 2012

Response by poster: The still-open question is: What is VZW's policy on all this?
I guess I could just try it, or I could ask at the Verizon store, but I'm wondering if the hivemind has any first-hand experience.

I just don't want to get stuck with an automated fee or something.
posted by jozxyqk at 7:22 AM on March 13, 2012

Response by poster: Sorry for babysitting my own thread, I knew I would do this :)

I went in to the VZW store and they told me that swapping a SIM from one VZW LTE phone to another VZW LTE phone _would_ work.. but not if I took the "phone SIM" and put it into a dongle or tablet, because they are "different codes in the system".

I will post another followup after I actually _try_ it (or to indicate that I chickened out) some point soon :)
posted by jozxyqk at 1:06 PM on March 13, 2012

Response by poster: Here's another followup:
I found a VZW LTE USB dongle, but unfortunately it uses full sized SIMs and my phone uses a micro SIM. So I wasn't able to test it, or maybe all dongles are like that just for that reason. Sigh.
posted by jozxyqk at 10:07 AM on March 17, 2012