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).
Answer: If you've bought an unlocked smartphone, you'll need a SIM (subscriber identity module) to get service. A SIM, sometimes called a SIM card, is a small card you slide into the phone (usually near the battery), that provides the phone with its phone number, as well as its voice and data service.nswer: If you've bought an unlocked smartphone, you'll need a SIM (subscriber identity module) to get service. A SIM, sometimes called a SIM card, is a small card you slide into the phone (usually near the battery), that provides the phone with its phone number, as well as its voice and data service.