There has been argument over whether or not cell phone cloning should be made illegal. Although it is commonly used as a means to induce phone fraud, others have argued that if someone owns a phone they should be able to clone their own phone, not making this a case of phone fraud. However, the general consensus is that the act of phone cloning is more commonly used as a means to commit phone fraud so generally it is considered a crime.
One of the best ways to avoid becoming a victim of phone cloning would be to avoid roaming. Criminals who commit cloning tend to target roaming locations like rural areas and airports and roaming also makes it hard for fraud preventing software to operate on a cell phone. Turning phones off when not in use also makes it less vulnerable to cell phone cloning. Also, using the security code or pin number that comes with the phone may not always protect from cloning, but it will help to better secure personal information.
It is also important to contact your cell phone provider immediately if your phone goes missing in an effort to either turn off your phone or to have on record in case cloning occurs. There also used to be devices for sale that would help criminals commit cell phone cloning, but they are now illegal to sell in the United States.