You might find that the network operator and their lawyers will be somewhat dipleased with your idea. SIMs and all of their imbedded information and encryption normally remain the property of the operator. Each SIM has a unique IMEI number which is linked to your also unique mobile number at their switch. These two numbers are coded together to allow the network to find you wherever you are in the worldwide GSM system (roaming agreements dependent). Operators can assign more than one mobile number to SIM (work number and after hours number = different tariffs) but not sure about the other way around. When you screw your card up by trying to hack the encryption, expect to fork out a new registration fee for the agro and be thankful you didnt get sued for breaching Intellectual Property Rights !! Another option: invest in a new car kit. ;-)