The following definitions captured in TR 21.905
a physically secure device, an IC card (or 'smart card'), that can be inserted and removed from the terminal. It may contain one or more applications. One of the applications may be a USIM.
Universal Subscriber Identity Module (USIM):
An application residing on the UICC used for accessing services provided by mobile networks, which the application is able to register on with the appropriate security.
Concerning the related service principles specified in TS 22.101
, some are still applicable while some may require careful review, for example
In TS 22.101, clause 13.3
"Terminals and Multiple UICCs" --
A single terminal may support the use of multiple UICC (e.g. with applications like USIM and/or banking, credit card, ...). Only one UICC shall be active at a time to access a PLMN.
In TS 22.101, clause 13.1.4
"Multiple USIMs per UICC" --
The standard shall support more than one USIM per UICC even when those USIMs are associated with different home environments. Only one of the USIMs or the SIM shall be active at a given time. While the UE is in idle mode, it shall be possible for the user to select/reselect one USIM application amongst those available on the UICC. At switch on, the Last Active USIM shall be automatically selected. The Last Active USIM shall be stored on the UICC. By default if there is no Last Active USIM defined in the UICC, the user shall be able to select the active USIM amongst those available on the UICC.
The standard must not prevent the coexistence of USIM applications, each associated with different home environments on the same UICC, so long as the security problems which arise from such a coexistence are solved.
The 3GPP system shall enable the secure support of an MUSIM UE with multiple USIMs from the same or different MNOs on the same UE.
The 3GPP system shall provide appropriate security mechanisms to prevent interference between operator's service preferences of one USIM and the operator's service preferences of the other USIM.
Each USIM shall appear as a separate device to the 3GPP system.