ETSI TR 131 901 presents a review of the USIM, ISIM and the related Toolkit aspects (respectively found in TS 31.102 [3], TS 31.103 [4] and TS 31.111 [5]) features and their mandatory/optional support in the light of actual use or demand in the field is to be conducted. The technical report documents the justification for the support of features identified as not being implemented or required (e.g. from SA1 requirements). When a common understanding is reached about a potential need for a modification of the required support of a feature, it will be listed for further consideration by CT6. Should any normative work be derived from the content of the study, it will be carried out as part of a separate work item.