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).
Version 25. The SIM card is the brain of your digital phone and gives you access to our advanced nationwide 4G network. The SIM card number is linked to your personal phone number, so you can call, text, browse the web, and more from just about anywhere.You can easily transfer it into other phones, retaining your personalized service information. Retail T-Mobile phones comes with a SIM card in the box.IM card types. Different phones use different kinds of SIM cards. To find out what kind of SIM card your phone is designed for, view the Tech Specs for your phone. Find them by clicking your phone on the Phones and Devices page.