Asked by: A J Lucas, Grimsby
SIM cards contain codes and numbers that allow them to access the network. The main identifier on the SIM card is a code called the International Mobile Subscriber Identity (IMSI). It's a 15-digit number where the first three digits identify the country, the next two yield the network and the final 10 are specific to your handset. It means that each country can potentially have 99 networks each with 999,999,999 subscribers. So, we'll have sufficient SIM combinations as long as no single country ends up with 100 billion mobile users. We should be fine for the time being!
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