I have read various articles about how you should not leave your old PC with just anybody, more specifically your hard drive, and use software like cyberscrub myself. I was not surprised to read that Smartphones retain extremely sensitive information about you, even after a reset. WashingtonPost explain how a Smartphone user had encrypted banking details but that emails, pictures and contacts were not properly deleted.
It seems understandable since the procedure of deleting files on a hard drive with a 3+7+3 type method or the Gutmann method to stop even hardware recovery are unknown to most people. Smartphones work in the same way as hard drives in that they use pointers a type of File Allocation Table to indicate where a file is. Deleting a file doesn't actually delete the data, it deletes the pointer that indicates where the file is in the memory. This means the file is still there and some clever software can retrieve it.
BlackBerry devices are in theory among the most secure of smart phones, Schroader said. However, those used by consumers lack the same security features as those used by government and private companies, Laudermilch said. "Even though there may be some security features on the device, most people don't know how or when to use them," he said.
Checking the specific Smartphone company support site often reveals how to properly erase your data should you want to part with the phone. Don't let your smart phone give away vital information about you !