Text 257, 145 rader
Skriven 2004-08-01 16:25:50 av Robert Bashe (2:2448/44)
    Kommentar till text 247 av Michiel van der Vlist (2:280/5555)
Ärende: Fido on the move via cell phone.
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Michiel van der Vlist wrote to Robert Bashe on Sunday August 01 2004 at 00:46:

[SIM card]
RB>> The only time you replace it is if you want to change providers or
RB>> want a new telephone number.

MV> Actuallly there is no technical need to change the SIM card fo r a
MV> change of telephone number. The telephone number is not on the SIM.
MV> The SIM contains the IMSI.

You've got it exactly backwards there, Michiel. The IMSI is in the phone
firmware, and the telephone number (the one you call) is on the SIM card. At
least that's the case with all the phones I've ever had or seen (Nokia 3310,
3330, Motorola T191). Remember, the IMSI is there to identify the phone.
Putting it on the SIM card would defeat that purpose, since throwing away the
SIM card would automatically remove the phone ID.

You can change the IMSI (depending on the country either illegal or frowned
upon, but it's possible) without having a SIM card at all. However, I don't
know of any way to program the SIM card to change the number, even if that
would be accepted by the provider.

MV> The link between the IMSI and the phone number is in the provider's
MV> Home Location Registry. The phone number can be schanged by editing
MV> the HLR. Not all providers offer that service though...

Never heard of that, and it would conflict with what I know about such phones
since in the above mentioned ones, you change the phone number (the one you
call, not the phone ID) by using a different SIM card.

As a matter of fact, the last time I checked (in 2003), most providers didn't
even check the IMSI. If they would, it would be easier to block stolen phones
from the network. And altered IMSIs would be easier to catch, since they would
generally match an existing one and be caught when two phones with the same
IMSI logged into the same network.

PK>>> .... or to upgrade to new features, or to replace a lost card.

RB>> Upgrade?

MV> From 8K to 32K memory?

??? I've never heard of this either, Michiel, but Peter writes it's done in
Norway.

RB>> Not that I'm aware. You really do have to buy a new phone for that,
RB>> since it's generally even impossible to flash new firmware (the flash
RB>> RAMs are intentionally made incompatible from model to model to
RB>> prevent a cheap phone from being upgraded to a more expensive one).
RB>> And to replace a "lost" card? How would you lose the SIM card in a
RB>> mobile phone without losing the phone too?

MV> By having two SIM's for different providers one phone?

OK, that's naturally possible, and I even know that you can get special
multi-SIM holders for some phones for the purpose, but I don't know anyone who
actually takes advantage of that option. Most everyone just has a phone with a
provider, and that's that.

RB>> A SIM card doesn't just "fall out" of the phone, since it's in some
RB>> kind of socket in the phone's interior.

MV> That indeed is unlikely, but some people frequently travel between two
MV> countries and they have a SIM card for each country.

Yes, Peter also explained that, and if you do that you naturally have such
problems. The only problem is the one I mentioned, that you have to keep
funneling money into the unused cards to keep them active. If you don't travel
very frequently indeed, this kind of thing would be pretty uneconomical even if
you _don't_ lose a SIM card.

MV> As for upgrades: I once had my SIM replaced by a so called dual card.
MV> A dual card is two SIM's with the same IMSI.

As I noted above, it's no problem (with some phones) getting a holder for more
than one SIM, and the IMSI is in the phone firmware so naturally it stays the
same for as many SIM cards as you can fit into the phone.

MV> My old phone (Sony CMD-X2000) became unstable for shirt pocket use but
MV> still worked fine in the car kit. I got myself a SIEMENS M35 for
MV> regular use.

I have a mobile phone, the Motorola T191, but practically never use it...
bought it more or less out of enthusiasm about the technology. The mobile phone
rates are simply too high for my taste, but I'm old-fashioned. I even get upset
at the prices of new cars and the fact that some 90% of all new cars sold in
Germany nowadays are equipped with an air conditioner (!?) - in _Germany_, the
land of rainy, cold summers, for cryin' out loud! But like I say, I'm old
fashioned and out of touch with the modern world...

MV> So instead of getting a new car kit, I got myself a dual card. One
MV> card is in the old phone that remains in the car, in the car kit, and
MV> the other card is in the "handy".

I suppose you can do that, but why not just buy a new phone? The older models
that "only" let you telephone other people (but don't play a symphony while
you're waiting, nor make coffee in the morning) are meanwhile quite
inexpensive.

MV> So instead of having to swap the SIM card, I just switch off the
MV> "handy" when I take the car. The phone in th ecar comes on when I
MV> switch on the ignition.

;-)

I've never felt the need to be "wired for sound" everywhere I go, but maybe
you're different - or maybe you too just do stuff like this because of
enthusiasm for the technology. It certainly is attractive.

MV> I should add that car kits are compulsory when using a phone while
MV> driving in The Netherlands.

If you use the phone while driving. That's also the case in Germany. But as I
say, I lived some 60 years without feeling the need to call or be called on the
phone while driving, and I suppose I'll continue that way for a while, so there
wouldn't be much point in this in my case.

MV> yes, the so called SIM lock. Originally meant as a deterrenty t theft,
MV> it was used by providers to discourage changing providers. here in The
MV> Netherlands providers were bound by law to supply the unlock code for
MV> free after one year.

Here it was (and is) two years. But many people simply "crack" the locks and
then use any SIM card.

MV> In the meantime the practise has vanished. One can now buy "naked" SIM
MV> lock free phones.

You can here too (in Germany), and they're not even that expensive anymore. But
of course, they don't make coffee for you in the morning either... ;-)

RB>> and this is often done (it's even legal to do so in the Netherlands,
RB>> where people offfer this service).

MV> Indeed it is. Or if one has enough courage one can hunt the web for
MV> the rquired software, get a "data cable" and do it oneself. I had my
MV> Siemens M35 unlocked that way. Didn't want to wait a year. I needed
MV> the data cable anyway to interface it to my laptop.

A practical option then.

Cheers, Bob

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