A general rule of thumb is that if your economic model has no value judgements, it's positive economics, and if it does have value judgements it's normative economics, since to tell someone what he ought to do, you first have to judge what is best for him.
A subscriber identity module or subscriber identification module (SIM) is an integrated circuit that is intended to securely store the international mobile subscriber identity (IMSI) number and its related key, which are used to identify and authenticate subscribers on mobile telephony devices (such as mobile phones and computers).
Without a SIM card, a GSM phone wonât be able to connect into any mobile network. The card is what holds all of the critical information. Each Sim contains a IMSI (International Mobile Subscriber Identity) and a authentication key that validates the IMSI. This authentication key is provided by the carrier. This is what allows your phone to be able to connect to the network & the this is the main purpose of the Sim card. Each SIM card has a unique identifier called the ICCID (Integrated Circuit Card Identifier), which is stored in the card and engraved upon it.