[Gta04-owner] Antwort: Re: Amazing adventures with a brandnew GTA04...

Christoph Mair christoph.mair at gmail.com
Sat Feb 11 20:06:30 CET 2012

On Sat, Feb 11, 2012 at 3:18 PM, Thomas Gstädtner <thomas at gstaedtner.net> wrote:
> Yes, SIMs are only used for identification, as the name suggests.
> In theory you don't need a SIM at all, and in many countries the
> providers allow phones to be used without SIMs - usually for emergency
> calls only.
> As providers usually allow you to use any device, they need the SIM
> registration to make sure they charge the correct party.
> The behavior that you can switch and it will work for a moment is
> unusual and likely modem and provider dependent.
> Checking the SIM is the modems job, and if it does not notice the SIM
> is missing and cache the relevant data on the SIM, there is no reason
> why it would not work for a while. The network itself does not care,
> the modem identified you and it is its job to answer.
> It would be Interesting if the behavior is the same if you don't
> switch from A to B but from B to A instead.

To exactly find out when the modem accesses the SIM you could use
SIMtrace: http://bb.osmocom.org/trac/wiki/SIMtrace


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