A ‘SIM’ or ‘USIM’ is an application, securely embedded in an UICC (Universal Integrated Circuit Card), which is the link between the subscriber to a cellphone contract and the service provider. It has some secure keys and algorithms on it that allow authentication to the radio access and core networks, plus other details related to the subscription It’s how the service provider ‘owns’ you, and can be moved from phone to phone.
Instead of a physical SIM eSIM technology uses an embedded chip which holds the same information that physical SIM contains which is being used by cellular operators for authentication and connecting to their server for making calls.
Traditional SIMs are operated by MNO/MVNO. If you want to change the provider, you have to change the SIM too. For embedded SIM, the user is able to get access to multiple mobile networks without changing the SIM card.
The eSIM stores one or more operator profiles. It is embedded or integrated in the device. Subscription changes are made over-the-air (remotely programmed). It ensures users always-on connectivity. Moreover, it enables good connectivity costs globally by using a mix of roaming and local subscriptions.
eSIM is rewritable, means you can change your operator just by downloading your new opearators profile into the eSIM.No more wating or putting SIM card inside the phone.
SO WHEN IT IS COMING ?
Currently eSIMs are supported only in 10 countries, India is recent entrant to the list. Recently launched iPhone 2018 series supports eSIM.
Austria, Canada, Croatia, Czech Republic, Germany, Hungry, India, Spain, United Kingdom and United States are the only countries in the world that supports eSIM.
iPhone XS, iPhone XS Max and iPhone XR supports eSIMs only for Reliance Jio and Airtel subscribers in India.
In the US, AT&T, T-Mobile USA and Verizon Wireless support eSIM. eSIM is backed by the GSMA, the association of mobile networks. The GSMA has defined the standadrd for eSIM worldwide.