So what can you do about all this the next time you’re ready to upgrade phones? The alarming answer is not much. According to Reiber, all of our volunteers did the right thing. They used the software tools available to restore each phone to its factory settings. But that didn’t matter. The data is still there, if you have the means to recover it. In fact, Reiber says there’s only one surefire way to make sure someone isn’t going to come along behind you and scarf up your old bits: Take a hammer to it.

via Break Out a Hammer: You’ll Never Believe the Data ‘Wiped’ Smartphones Store | Gadget Lab | Wired.com.

Another reason not to use your mobile gadget for storing any sensitive information.  Here’s a link to MPE+ Mobile Phone Forensics mentioned in the article.  Here’s a sample of their features:

PHYSICAL IMAGING OF ANDROID DEVICES

MPE+ enables physical imaging of Android devices. MPE+ features built in rooting functions that allows the physical analysis of any partition on an Android device. No need to pay for additional “rooting” suites.