Abstract: During the invent of Code Division Multiple Access (CDMA) mobile phones, no one could ever imagine a day would arise,when more than a billion mobile phones would be manufactured and used worldwide over a short span of time. Each mobilephone is required to have a unique serial number burned into its chips in order to prevent fraud. Without a unique number, the phone can't be sold. So initially in order to identify phones on a network, engineers developed a 32-bit code called the Electronic Serial Number (ESN). This code was used for billing and to make sure the right call went to the right phone. But 32 bits only allowed 4 billion unique numbers; engineers probably didn't forecasted ESN to be a long-term solution.