Patent ID: 6934391

Claim:
A method, for use in a mobile data communication system that includes: first and second subscriber registers (HLR 1 , HLR 2 ) for maintaining subscriber records; a message transmission system (SMSC) for transmitting messages in the communication system; and a mobile station (MS) for use by a subscriber in effecting mobile communications through said mobile data communication system said method being for controlling a subscriber identity module (SIM) attached to said mobile station (MS), in which subscriber identity module (SIM) is stored subscription data comprising a first subscriber identity code (IMSI 1 ) and an encryption code key (K i ) corresponding to a first subscription for the mobile station subscriber such that when said first subscription is opened for said mobile station subscriber, a record of data corresponding to said first subscription, with said record comprising: a first subscription-specific call number (MSISDNx), said encryption code key (K i ), and said first subscriber identity code (IMSI 1 ) for said mobile station subscriber, is created in said first subscriber register (HLR 1 ); said method comprising the steps of: a.) opening a second subscription for said mobile station subscriber; b.) creating in said second subscriber register (HLF 2 ) a record of data corresponding to said opened second subscription, and comprising: a second subscription-specific call number (MSISDN), said encryption code key (K i ), and a second subscriber identity code (IMSI 2 ) for said mobile station subscriber; c.) transmitting through said mobile data communication system to the mobile station (MS) a message (SMS) addressed to said first subscription-specific call number (MSISDNx), said message instructing to change said first subscriber identity code (IMSI 1 ) comprised in said subscription data stored in said subscriber identity module (SIM) into said second subscriber identity code (IMSI 2 ); and d.) changing, at said subscriber identity module (SIM) attached to said mobile station (MS) and in response to receipt of said message (SMS), said first subscriber identity code (IMSI 1 ) into said second subscriber identity code (IMSI 2 ).