Sim card cloning is true. Review on Tips on SIM cards

Phone cloning involves placing a computer chip into the target mobile telephone, allowing the electronic serial number (ESN) of the mobile phone to be modified. The ESN is normally transmitted to the cellular company in order to ascertain whether the mobile phone user is the legitimate owner of that phone. Modifying this, as well as the phone number itself (known as the mobile identification number, or MIN) paves the way for fraudulent calls, as the target telephone is now a clone of the telephone from which the original ESN and MIN numbers were obtained.

Cloning has been shown to be successful on code division multiple access (CDMA) but rare on the Global System for Mobile communication (GSM), one of the more widely used mobile telephone communication systems [ 1 ] . However, cloning GSM phones is achieved by cloning the SIM card contained within, not necessarily any of the phone's internal data (GSM phones do not have ESN or MIN, only an IMEI number.) There are various methods used to obtain the ESN and MIN; the most common are to crack the cellular company, or eavesdrop on the cellular network. GSM SIM cards are actually copied by removing the SIM card and placing a device between the handset and the SIM card and allowing it to operate for a few days and extracting the KI, or secret code[ citation needed ].

This is normally done with handsets that have the option of an "extended battery" by placing the normal size battery in the handset and the Kopy Kat in the now vacant extra space. This is done by allowing the device to log the interaction between the mobile telephone switching office and the handset.