A mobile device of a person is the key to all his secret information that if falls into wrong hands can be the cause of hazardous situations. So if you are planning to sell off your mobile phone or even exchanging it for a brand new one make sure to data wipe from mobile phones completely. There have been several scams that have come forward where people buy used mobile phones from unsuspecting people by showing off better products and in the excitement of the new device people tend to forget to erase or transfer the important data from their old phone before handing it over to the buyer. So it is an absolute necessity that whether your device is an android or an IOS device, the data on the device is either transferred on the new device or erased off the memory of the old device completely. The same stands true in case of computer recycling.
But before you start wiping off the data off your phone you may want to keep a few things in mind like:
Android:
If you own an android device he simplest way is to perform a factory reset but it is also true that this erases just the data stored in the applications of the phone. To completely erase or remove the complete data from your phone you can begin by encrypting the android device from the settings of the phone and settling down patiently to watch the data being erased from your phone.
IOS
When wiping off the data from an IOS device make sure to turn off all the services in the device. you can start by the Find my iPhone service which can be found in Settings under iCloud. Make sure to sign out of iCloud completely because if you manually delete all the data without signing out of iCloud you are bound to lose the complete data permanently. After turning off and logging off from services like iMessage and Apple ID start the wipe process.
Source : http://datawipe.webnode.com/data-wiping-is-a-must-before-selling/