SIM card locked to provider?

A real basic question...

If I buy a used AT&T GSM phone that is unlocked, do I need to buy a SIM card
from T-Mobile if that is my carrier of choice? Or can the SIM be used for
more than one carrier?

In other words, when changing carriers, does one need to get a SIM card
branded by the new carrier?

FBt

On Sat, 05 Jan 2008 09:01:55 GMT, Esther & Fester Bestertester
<not@me.really> wrote:

>A real basic question...
>
>If I buy a used AT&T GSM phone that is unlocked, do I need to buy a SIM card
>from T-Mobile if that is my carrier of choice? Or can the SIM be used for
>more than one carrier?
>
>In other words, when changing carriers, does one need to get a SIM card
>branded by the new carrier?

The SIM card is issued by the individual carrier, and allows the phone
to register with that carrier only.

Chris

In <l3run3d1ni4avjefi1hf870200du0r5aco@4ax.com> Chris Blunt <chris_blunt@spamfence.net> writes:
>>
>>In other words, when changing carriers, does one need to get a SIM card
>>branded by the new carrier?

>The SIM card is issued by the individual carrier, and allows the phone
>to register with that carrier only.

With the slight exception that many carriers have "roaming"
arrangements/partners, especially in areas where one
has coverage and the other doesn't.

But in general, you're best off, by far, in getting
the SIM issued by the carrier you want to use.

--
__________________________________________________ ___
Knowledge may be power, but communications is the key
dannyb@panix.com
[to foil spammers, my address has been double rot-13 encoded]

>> The SIM card is issued by the individual carrier, and allows the phone
>> to register with that carrier only.

> With the slight exception that many carriers have "roaming"
> arrangements/partners, especially in areas where one
> has coverage and the other doesn't.
>
> But in general, you're best off, by far, in getting
> the SIM issued by the carrier you want to use.

Thanks. That is teh definitive (if not the desired) answer I was looking for.
FBt

Esther & Fester Bestertester wrote:
> A real basic question...
>
> If I buy a used AT&T GSM phone that is unlocked, do I need to buy a SIM card
> from T-Mobile if that is my carrier of choice? Or can the SIM be used for
> more than one carrier?
>
> In other words, when changing carriers, does one need to get a SIM card
> branded by the new carrier?

SIM = Subscriber Identity Module. The required information for your
phone to request access is stored in the card, each time you turn the
phone on it attempts to register with networks within range. This is
only possible if it is the HOME network of your provider, or if there is
a roaming agreement with another network in range otherwise you will not
be able to make or receive calls.

Except 112 (standard GSM Emergency number), which is normally redirected
to the local Emergency number. If you are lucky the local Emergency
number is also mapped into the phone to work as 112. It is good
practice to dial 112 on a GSM phone as it flags the call as an EMERGENCY
call and will log into any network available and if required drop other
normal calls on that cell if required to initiate and maintain the
EMERGENCY call.


--
The views I present are that of my own and NOT of any organisation I may
belong to.

73 de Simon, VK3XEM.

["Followup-To:" header set to alt.cellular.]
On 2008-01-06, Simon Templar <usenet@vk3xem.net> wrote:


> Except 112 (standard GSM Emergency number), which is normally redirected
> to the local Emergency number. If you are lucky the local Emergency
> number is also mapped into the phone to work as 112. It is good
> practice to dial 112 on a GSM phone as it flags the call as an EMERGENCY
> call and will log into any network available and if required drop other
> normal calls on that cell if required to initiate and maintain the
> EMERGENCY call.

The OP was talking about T-Mobile and AT&T. AT&T is an American provider and
the Emergency number here is 911, not 112. I assume that since AT&T was
mentioned, the OP was talking about T-Mobile USA and not some overseas
division of T-Mobile.

Other than that, I agree with what you said.


--
Steve Sobol, Victorville, CA PGP:0xE3AE35ED www.SteveSobol.com
Geek-for-hire. Details: http://www.linkedin.com/in/stevesobol

Steve Sobol wrote:

> ["Followup-To:" header set to alt.cellular.]
> On 2008-01-06, Simon Templar <usenet@vk3xem.net> wrote:
>
>
>> Except 112 (standard GSM Emergency number), which is normally
>> redirected to the local Emergency number. If you are lucky
>> the local Emergency umber is also mapped into the phone to
>> work as 112. It is good practice to dial 112 on a GSM phone
>> as it flags the call as an EMERGENCY call and will log into
>> any network available and if required drop other normal calls
>> on that cell if required to initiate and maintain the
>> EMERGENCY call.
>
> The OP was talking about T-Mobile and AT&T. AT&T is an
> American provider and the Emergency number here is 911, not
> 112. I assume that since AT&T was mentioned, the OP was
> talking about T-Mobile USA and not some overseas division of
> T-Mobile.

On a GSM phone, if dialling 911 provides the same functionality
as dialling 112, then that's because 911 is listed in the SIM's
EF_ECC (emergency call codes) file, at SIM address 6FB7.

John

danny burstein wrote:

> All recent (?5 years?) GSM phones in the US will let
> you call out to 911 and 112 (which gets translated
> to 911) with or without a SIM, and whether or
> not that SIM is activated. (Provided, of course,
> that you're in radio range of a compatable GSM
> base station).

In the US, the translation will be from 911 to 112 (the GSM
distress-priority number) prior to the call being placed, and
then to 911 when the call hits the fixed telephone network.

Modern GSM phones will often have 911, 999 and 000 entered into
the SIM's EF_ECC file. So these and 112 will provide identical
functionality. You may be able to dial them and connect even
with the keypad locked.

John

Simon Templar wrote:
> Esther & Fester Bestertester wrote:
>> A real basic question...
>>
>> If I buy a used AT&T GSM phone that is unlocked, do I need to buy a
>> SIM card from T-Mobile if that is my carrier of choice? Or can the SIM
>> be used for more than one carrier?
>> In other words, when changing carriers, does one need to get a SIM
>> card branded by the new carrier?
>
> SIM = Subscriber Identity Module. The required information for your
> phone to request access is stored in the card, each time you turn the
> phone on it attempts to register with networks within range. This is
> only possible if it is the HOME network of your provider, or if there is
> a roaming agreement with another network in range otherwise you will not
> be able to make or receive calls.
>
> Except 112 (standard GSM Emergency number), which is normally redirected
> to the local Emergency number. If you are lucky the local Emergency
> number is also mapped into the phone to work as 112. It is good
> practice to dial 112 on a GSM phone as it flags the call as an EMERGENCY
> call and will log into any network available and if required drop other
> normal calls on that cell if required to initiate and maintain the
> EMERGENCY call.


I'm unaware of any cell-based priority of 911 calls over any other call.
Certain IMEI codes can be assigned a higher access priority over other
IMEI codes, but this higher access priority would apply whether the
special IMEI handset called a hospital or the local crack dealer.


--
jer
email reply - I am not a 'ten'

Jer wrote:

> I'm unaware of any cell-based priority of 911 calls over any
> other call.
> Certain IMEI codes can be assigned a higher access priority
> over other IMEI codes, but this higher access priority would
> apply whether the special IMEI handset called a hospital or
> the local crack dealer.

In the more usual configuration, a phone of any access class can
make an emergency priority call. All that's required is that
the user dials 112 or a number in the SIM's EF_ECC file.

If there's no SIM fitted, then the handset itself might be able
to do an equivalent lookup of predefined emergency numbers in
firmware. So a call to 911 in a handset without a SIM _might_
be treated as an emergency call within the radio layer, and
connected with priority. Such a call will connect you to
emergency services however, rather than your prefered dealer.

While GSM 04.08 does allow for access to the emergency call
facility to be restricted to access classes 11 through 15, that
restriction is not normally in place.

John