[SHR] Revealing/Hiding my caller id

Helge Hafting helge.hafting at hist.no
Thu Feb 26 12:29:43 CET 2009

Franky Van Liedekerke wrote:
> On Wed, 25 Feb 2009 15:39:17 -0600
> The Digital Pioneer <digitalpioneer at gmail.com> wrote:
>> Ahh, too bad. :P
>> I don't suppose anyone could mod the firmware to make it allow that
>> could they? It would be a fun prank. :)
> it sounds to me that it would totally and utterly illegal ... I can't
Not necessarily illegal, but probably breaking the contract with
your service provider. Providers aren't known for appreciating creativity.

Having the call billed to someone else, or impersonating someone else is 
obviously illegal. Having the caller ID come up with something obviously 
fake like "000000" is not so bad legally. You are allowed to hide 
completely, after all.

Having caller ID showing one of your other phones so they return calls 
there instead is even useful. But anything useful is precisely the sort 
of thing a service provider will want to bill you extra for.

> even begin to imagine how criminals would abuse such a thing.
Truly untraceable calls with ever-changing IMEI, never paying for 
service, optionally bill it all to someone you dislike, intercepting 
calls, DOS-attacks on gsm, . . .

> And I'm not even sure that you can do it by changing firmware, there's
> always a man in the middle (the GSM provider) that normally sends your
> phonenumber to the other party (except if you indicate you don't want
> it).

In theory, the GSM provider could validate all that happens. In practice 
they don't, probably because there were some things they didn't think of 
when they implemented their towers. A user-flashable gsm firmware is a 
more recent development than GSM technology.

I once called the police about a bothersome anonymous caller. When the 
telco eventually tried, they actually failed to trace it. They claimed 
the caller was a mobile phone whose subscription ended two years earlier 
which couldn't be right. You can't normally call out unless you pay for 
some kind of subscription.

GSM history also have its share of goofups. Some years ago, it was 
possible for norwegians to get free calls in some eastern europe 
country. I don't remember the details, something about two different 
national telcos that just happened to have the same numerical ID. With 
things like that happening by accident, no surprise that determined 
hackers can get further.

So phone hacking is definitely possible. There are probably some shady 
websites with more information too.

Helge Hafting

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