A search on the Internet also reveals websites openly selling cloning and SIM-card backup softwares readily available. Run a search on Google and after some tries, you will surely find some software which will let you clone mobiles! Yes there are many softwares and chips available on the Internet which allows you to clone a SIM card into another SIM card. Eventually there are also many other websites which sell chips which can be programmed into SIM card using their software!
Each cellphone has an erasable-programmable read-only memory (EPROM). You can call it as the nucleus of the phone. This chip contains the cellphone's electronic serial number (ESN) and electronic machine identification number (EMIN). The EMIN is comparable to the DNA that makes an individual unique. There are even more numbers related to SIM and mobiles which collectively make a mobile equipment unique to the world (and of course to the cellphone operators). The problem with this model of mobility is that even the cellphone's operators can't distinguish a cloned phone from a genuine one.
This crime is said to be pretty easy to commit and one can easily clone a mobile. At the first glance, a newbie can think that this must be a matter involving all sort of programming and hardware information on the Mobile's architecture but they are wrong. Cloning doesn't require one to be a hardware engineer of a mobile nor does he need to be a programmer. All of the cloning can be done via the softwares available for this purpose. Many such softwares are designed in a way that anyone just needs to connect two phones simultaneously to a computer or one by one and the rest will be done by the software itself. However one of the famous softwares (name will not be disclosed) gave the user all the important information about the mobile which was connected to the computer. There are a lot of softwares available for download which can do the same. Now think of the risk if your mobile gets into the hands of any person who has a computer and knows the important numbers required cloning a mobile! Any such person can download software for the purpose or better buy a chip which can be programmed as a SIM and later be used to inflate your bills.
However some people will claim that most of the numbers which make a phone identified over a network is generated in combination with unique identities of SIM as well as phone, so the cloned mobiles can be caught or will not work. I ask them a humble question: say you changed the handset and used the same SIM in the new handset; will your phone work in this case? Yes, it will. So will it work in case of cloned mobiles? The numbers which are generated in combination with the identities of both the SIM and the phone are generated for temporary use or we can say that they are significant for only a "talk session". So it should be very well understood that every phone is at risk!
Unscrupulous cellphone dealers and repairers who have access to the ESN and EMIN of someone's cellphone may offer them to the people who can clone mobiles. Sometimes the information is obtained from service providers. Using special software, the cloner embeds these numbers on the EPROM of another cellphone, from which a user can make calls for which someone else pays.