A mechanism for releasing a SIM card locked into an electronic device, said mechanism including: - a SIM card holder comprising a substantially rectangular frame made up of an external cover that closes an access opening formed in a device case, two legs extending orthogonally from said external cover into said device case and an internal side orthogonally connecting said two legs, said holder defining a SIM card receiving space, SCRS, located adjacent to the external cover; - a mechanical restraint that keeps the SIM card holder locked inside the device such that the external cover is flush with the external surface of the device case; - a shape memory alloy actuating element, preferably in the form of a shape memory alloy wire, that upon activation releases said mechanical restraint; - elastic means for the ejection of the SIM card holder upon release of the mechanical restraint; characterized in that - said mechanical restraint is spring-loaded; - said internal side of the holder frame has at least one spring-like flexible portion that allows a longitudinal contraction of said internal side; - the shape memory alloy actuating element extends between the two legs of the holder frame, preferably orthogonally thereto; - the SIM card receiving space, SCRS, is extended along the two legs, either in the length direction or in the thickness direction, such that a SIM card fitted therein does not prevent said longitudinal contraction of the internal side; and in that said mechanism further includes - two conductive pads arranged adjacent to the access opening of the device case; and - two conductive strips arranged on the holder frame along the two legs respectively, said conductive strips extending between the ends of the shape memory alloy actuating element and the end portions of the external cover at a position in correspondence with said conductive pads. - a SIM card holder comprising a substantially rectangular frame made up of an external cover that closes an access opening formed in a device case, two legs extending orthogonally from said external cover into said device case and an internal side orthogonally connecting said two legs, said holder defining a SIM card receiving space, SCRS, located adjacent to the external cover; - a mechanical restraint that keeps the SIM card holder locked inside the device such that the external cover is flush with the external surface of the device case; - a shape memory alloy actuating element, preferably in the form of a shape memory alloy wire, that upon activation releases said mechanical restraint; - elastic means for the ejection of the SIM card holder upon release of the mechanical restraint; - said mechanical restraint is spring-loaded; - said internal side of the holder frame has at least one spring-like flexible portion that allows a longitudinal contraction of said internal side; - the shape memory alloy actuating element extends between the two legs of the holder frame, preferably orthogonally thereto; - the SIM card receiving space, SCRS, is extended along the two legs, either in the length direction or in the thickness direction, such that a SIM card fitted therein does not prevent said longitudinal contraction of the internal side; - two conductive pads arranged adjacent to the access opening of the device case; and - two conductive strips arranged on the holder frame along the two legs respectively, said conductive strips extending between the ends of the shape memory alloy actuating element and the end portions of the external cover at a position in correspondence with said conductive pads.