This set is all what you need to get started with SIM cloning. You will get one 12-in-1 blank Multiple SIM card, one USB SIM card manager and one companion CD.
Multi SIM technology is an amazing thing. You can clone up to 12 GSM SIM cards (of format COMP128v1) into one Multi SIM card. After that you can leave your original SIM cards in some secure place at home and use only the Multi SIM card in your day to day life.
Multi SIM card allows switching between (up to) 12 stored numbers right from your phone's main menu (a new menu entry in your phone will automatically appear after you insert the Multi SIM card into your phone). You don't need anymore to extract the phone's battery or even to turn off and on the phone in case to change the number!
At a time only one of the cloned phone numbers may be active, all other cloned phone numbers will be unavailable as if they were turned off.

The Multi SIM technology is for several years here now and is a result of a poor security algorithms used in the encryption of the first generation of GSM SIM cards, what is also commonly called COMP128v1. Since then, the SIM cloning is now more difficult to perform, as more and more mobile operators are moving towards newer generations of encryption methods used in GSM SIM cards (like COMP128v2 or COMP128v3). But SIM cloning is still possible in with some operators in some countries like Russia, Iran, China and so on. SIM cards issued before June 2002 most likely are COMP128v1 SIM cards, thus clonnable.
Multi SIM technology of programming information from several SIM cards into one multi functional SIM card has nothing to do with the Multisim™, which is a respective property and trademark of National Instruments.
Comments
SIM Cloning doesn't work in Europe
I just wanted to notice that SIM cloning is not appliable to most of the European operators because few years ago they switched to more advanced encryption algorithms for SIM cards.
Not really correct
Stating that multisim technology doesn't apply to Europe is not correct. There are still a lot of european mobile operators, which are multisim-able. For more information check this user forum: http://www.gsmhosting.com/vbb/showthread.php?t=213686