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).
SIM cards are the most important part of a cell phone that runs on a GSM network. They enable the phone to receive signal from a mobile phone company.Many people who have phones that accept SIM cards find it extremely easy to simply swap out their SIM card for a new SIM card when in a different country.hen you open up the back of a phone that is equipped with a SIM card, you will see the card tucked into the phone. Usually, the card is tucked behind the battery. SIM cards are also great because they can be used with any handset that accepts them.