!!! Overview[1]
[{$pagename}] ([UICC] Commonly known as a [SIM] card) is the [Smart Card] used in [Mobile Devices] in [GSM] and [UMTS] networks. Commonly known as a [SIM] card, although it is technically a [SIM] only when used on [GSM] networks and the [USIM] works on [UMTS] networks.

Any modern mobile device nowadays has an [{$pagename}] of some form or another. 

[{$pagename}] are actually [Smart Cards] that can host applications, and as such are one form of a [Secure Element]. However, since the [{$pagename}] is only connected to the baseband processor, which is separate from the application processor that runs the main device [Operating System], they cannot be accessed directly from [Android]. Typically, the [{$pagename}] must be accessed by the __OWNER__ of the [{$pagename}] which is the [Mobile Network Operators] or in [IOS], [Apple]

All communication to the [{$pagename}] __MUST__ to go through the [Radio Interface Layer] ([RIL]) which is essentially a proprietary [IPC] interface to the baseband processor. 

Communication to the [UICC] [Secure Element] is carried out using special extended AT commands (AT+CCHO, AT+CCHC, AT+CGLA as defined by 3GPP TS 27.007).

[{$pagename}] ensures the [integrity] and security of all kinds of [personal data], and it typically holds a few hundred kilobytes. 

With the advent of more services, the storage space will need to be larger.

In a [GSM] network, the [UICC] contains a [SIM] application and in a [UMTS] network it is the [USIM] application. 

!! More Information
There might be more information for this subject on one of the following:
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* [#1] - [Accessing the embedded secure element in Android 4.x|http://nelenkov.blogspot.com/2012/08/accessing-embedded-secure-element-in.html|target='_blank'] - based on 2015-01-09
* [#2] - [Subscriber_identity_module|Wikipedia:Subscriber_identity_module|target='_blank'] - based on information obtained 2016-08-15