GSM Tech

Piotr Duda openmoko at
Sun Dec 16 02:30:35 CET 2007

Dr. H. Nikolaus Schaller pisze:
> The phone is locked so that it can be used only with a specific SIM. So,
> the SIM is the key to make the phone useable. Therefore, a SIM-lock
> (well it should be called SIM-key).

The phone is locked so it can be used only with SIM cards of specific operator.
Of course one can imagine a soft in the phone that locks on the first inserted
SIM card but it just doesn't work like that.
When U go to your gsm operator's shop and want to change your phone U just get
shinny new one just from the shelf, sign your new contract for the next year or
two, and pretty smiling lady helps you to put your old SIM card into new phone.
Now you can give your old phone to your son or grandma. But wait, U have to buy
a prepaid card or sign another pact with a devil, sorry, with the same operator
to do it.

> Why? It is a feature of the GSM security system. And - there are modules
> in GSM-CF cards format. There, the operating system is called "Windows",
> "Linux", "MacOS". And, they clearly have no support for SIM-locks.

IMO it is done in the software of the phone (well in phone's operating system).
How do you expect that FCC allows some phone to the US market with awareness that
that many US operator's employees will have full access to GMS's firmware. I don't
believe in that. We all know, that all or almost all GSM operators puts their own
versions of phone software into the phones they are going to sell. It can contains
some additional menus, operator's logo at background and in screensavers and so on.
And here is also a place to put some SIM-lock stuff.

I have also heard that in some models unlocking is as simply as entering some code.
But in most of them AFAIK you need to some special software. But do you think that
phone's software of the former is specially prepared to modify GSM firmware when user
enter special code? It seems very unlikely to me :).


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