If someone manages to get access to my iPhone's SIM card (I left the phone at a repair shop for a few days and forgot to take the SIM card out).

Now, the repair people at that shop were acting all shifty when I picked up the phone and quoted really outrageous prices for parts replacement for it to be fixed (including the motherboard). So I didn't have them do any work on it.

I was just wondering if they cloned my SIM card or something, because now that I got a new phone on the same line (same number) I'm getting occassional calls from some foreign number with a foreign country code.

Will getting a new / replacement SIM card for the same number cancel out their cloned card (if it was indeed cloned? and block them forever?

closed as too broad by user45139, Neil Smithline, Steve, user10008, Xander Oct 20 '15 at 23:10

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • 2
    Call your provider, better to be safe than stuck with a huge bill. – Jay Oct 20 '15 at 8:27
  • SIM cards aren't simple to copy. And two phones with the same SIM card will set off alerts at the phone provider. – Neil Smithline Oct 20 '15 at 18:09
  • 2
    I think this question needs to be answered by your phone provider. – Neil Smithline Oct 20 '15 at 18:09
  • What was the price? How outrageous was it compared to competitors? – MonkeyZeus Oct 20 '15 at 19:28

A mobile phone, generally speaking (*), is broadcasting the message "the SIM card I have with the ID XXXX is now available on the network". This ID is called IMEI IMSI (**) and is unique to a SIM card.

The IMSI is then mapped to a phone number by your provider.

If you break this chain (by going to the network provider and requesting a new SIM card) the cloned card is useless: its IMSI stops to be associated with your phone number (which you may still keep on the new SIM card).

The technical corner: cloning a card into a functioning one is not a simple task (particularly if the card is protected by a PIN). It requires rogue cooperation with the network operator but once such a card is available, it is placed in a SIM-dialer - a device which continuously dials premium (expensive) numbers so that you run out of credit. This is why it is important to have it blocked as soon as possible, especially when you are in a foreign country. Fun fact: this SIM dialer is called in French a "pondeuse", which refers to a hen laying eggs.

That was for the "someone could call on my behalf" part.

You also mention that you are now getting calls from unknown numbers. These calls are not a danger, they are just particularly annoying. You can try to add them to your automatic rejection list and if they persist, then the only way is to change your number (which can be done without changing the SIM card, per above).

The shop may have given your number to scammers, you will never know. Or it may just be a coincidence.

As a side note, beware of calls which just ring once or twice, trying to get you to call back (or if you pick the phone up, there is a generic message like "I cannot hear you, hello? hello? Please call back this is important"). There are usually two categories of such scam calls:

  • the ones which show a local number. If you call that number you get a message of the type "you have received a voice mail, please dial to retrieve it"
  • the ones which show a premium number with the international prefix for your country. The idea is that when you live for instance in France (prefix +33) you may be less reluctant to call back +33899235467 than an well-advertised 0 899 ... which is more recognizable as an expensive (premium) number.

(*) "generally speaking" means that what follows is mostly correct, there are many simplifications and some inaccuracies but you should get the whole picture.

(**) I initially wrote by mistake "IMEI" instead of IMSI. The IMEI is another identifier, unique unique to the phone itself (not the SIM). Its uniqueness is supposed to help to blacklist a stolen phone but it usually does not work (either the blacklisting is not applied by the carrier, or is reset by the thieves to something else).

  • I was about to mention in my (**) that the IMEI is used to block (hopefully) phones when I saw a comment right about that - which is now deleted? I will add the info anyway – WoJ Oct 20 '15 at 14:50
  • Yeah, that was me :) I posted my comment within seconds of you changing IMEI to IMSI, so I thought it wasn't relevant any more. – bob esponja Oct 20 '15 at 15:00

Does your phone require entering a PIN code on startup? Is your SIM card less than 10 years old? If this is the case, you're almost certainly safe.

In fact, if your SIM card is recent (approx. 2005 and up), it's most probably unclonable even if you don't require a PIN on startup. Cloning was really an issue for old COMP128v1 SIMs. Newer SIMs are designed to resist cloning even by the legitimate owner, otherwise mobile providers themselves would be abused by users paying for a single SIM card and using multiple phones simultaneously.

Note that if your SIM card doesn't require a PIN on startup, shop personnel may have abused it by simply calling premium numbers or abroad, even if they didn't manage to clone it.

Not the answer you're looking for? Browse other questions tagged or ask your own question.