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).
Definition: SIM Card â SIM is short for Subscriber Identity Module. SIM cards are small removable smart cards that are used in many cell phones to store data like a customer's mobile phone number, the mobile phone company they use, and address book information.ome phones have what is called a SIM lock, a feature that uses the SIM to tie the mobile phone to a specific phone company (usually the one who the user bought the phone from originally).