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ronniemckenna
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How does virgin sim card know if the phone is blocked/ blacklisted?

Hi,

I am hoping someone could walk me through the steps a sim cards takes once it has been inserted in a phone. 

Specifically I am looking for answers to these questions below too. 

(1) Once simcard is in phone how does it decide if it is eligible to "speak" to handset?

(2) How does a sim card know if a phone IMEI has been  blacklisted?

(3) If a phone's IMEI number doesn't appear on the virgin media database will the sim card and phone be incompatible? 

I recently purchased a phone to use with my pay monthly contract until I can get an upgrade. The phone is unlocked to any network and indeed works with every other UK network provider apart from Virgin. I am trying to understand the mechanics of the simcard/ handset relationship to determine if virgin sims do some part of the prcess slightly different which prevents the two from working.  

All advice/ info greatly appreciated. I'm determined to get to the bottom of this as I am intrigued with the problem... not to mention I love the phone and would hate to have to give it away/ or change provider). 

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Superuser
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Re: How does virgin sim card know if the phone is blocked/ blacklisted?

Your kind of coming at it from the wrong angle

A SIM card is nothing to do with an IMEI number

In REALLY simple terms

The SIM card contains the information a GSM unit needs to connect to a network.

An IMEI is just a unique identifier for the device. If you are familiar with computers, think IP address and gateway (SIM)  and MAC address (IMEI)

The SIM card tells the  phone HOW to connect to a network- the network then decides if the IMEI is blacklisted or not (i.e stolen, prevented from connection to that network for other reasons)

there is a third number, the IMSI, which allows a SIM lock to work. Unlocking a phone involves removing restrictions by IMSI so in most cases an unlocked phone SHOULD work with any provider.

So the balance of probability is that the VM SIM is not valid, rather than the actual handset  being unable to connect to VM's network. Especially as VM's network piggybacks on EE.

The exact mechanics of how all this works are covered fairly well at

https://en.wikipedia.org/wiki/Subscriber_identity_module

https://en.wikipedia.org/wiki/International_Mobile_Station_Equipment_Identity

https://en.wikipedia.org/wiki/SIM_lock

 

 


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ronniemckenna
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Re: How does virgin sim card know if the phone is blocked/ blacklisted?

Hi thanks for the quick response. 

What do you mean by "the VM sim card is not valid?".  

Thanks for the info so fat, much appreciated. 

 

Ronnie. 

 

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Superuser
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Re: How does virgin sim card know if the phone is blocked/ blacklisted?

Every SIM card has unique identifiers that the network recognises. So a SIM that has been either blocked off the network, or has expired (PAYG with no top up for  x number of months) will NOT allow a connection to be made, no matter what phone you put it in.

So you can check easily, pop it into a different unlocked phone. If it doesn't work, its the SIM card.

If the phone will connect to other UK networks with a different SIM card in it (as you have stated), its likely the SIM card at fault, not the IMEI being blocked.