A method for performing secure change of operational mode of a multi-SIM telecommunications device , the method comprising: enabling each of a plurality of modem modules of the telecommunications device in a limited operational mode; performing a first verification, by a first authentication module of a plurality of authentication modules of the telecommunications device, to verify the validity of a first subscriber identity module associated with a first modem module of the plurality of modem modules in accordance with network configuration information, wherein responsive to a positive first verification the first modem module is transitioned to an enhanced operational mode and the first modem module performs a network attachment procedure to a first network using the first subscriber identity module; performing a second verification to verify active attachment of the first modem module to the first network in accordance with the network configuration information; providing the result of the second verification to a second authentication module of the plurality of authentication modules; performing a third verification, by the second authentication module, to verify the validity of a second subscriber identity module associated with a second modem module of the plurality of modem modules based on the network configuration information, wherein responsive to both a positive second verification of the first modem module and a positive third verification, the second modem module is transitioned to an enhanced operational mode and the second modem module performs a network attachment procedure to a second network using the second subscriber identity module. enabling each of a plurality of modem modules of the telecommunications device in a limited operational mode; performing a first verification, by a first authentication module of a plurality of authentication modules of the telecommunications device, to verify the validity of a first subscriber identity module associated with a first modem module of the plurality of modem modules in accordance with network configuration information, wherein responsive to a positive first verification the first modem module is transitioned to an enhanced operational mode and the first modem module performs a network attachment procedure to a first network using the first subscriber identity module; performing a second verification to verify active attachment of the first modem module to the first network in accordance with the network configuration information; providing the result of the second verification to a second authentication module of the plurality of authentication modules; performing a third verification, by the second authentication module, to verify the validity of a second subscriber identity module associated with a second modem module of the plurality of modem modules based on the network configuration information, wherein responsive to both a positive second verification of the first modem module and a positive third verification, the second modem module is transitioned to an enhanced operational mode and the second modem module performs a network attachment procedure to a second network using the second subscriber identity module. <EOS>