Are Text Messages Stored in the Phone Even If You Delete Them?by Micah McDunnigan
Just because you don't see your text messages anymore doesn't mean they aren't hiding somewhere in your phone. Deleting a text message on your phone makes the device forget about the message, but the data for the message itself can continue to linger in your device's memory.
Data Storage and Deletion
Electronic devices store data, like text messages, across certain memory addresses and make internal notes about what data is stored where. If the device has recorded that data is stored at particular memory locations then it makes sure not to use them for future data storage. When you tell the device to delete data, what it does is remove the entry about the data stored at those addresses from its records. As far as the device's operating system is concerned, the memory at those locations is empty. However, the raw data is still sitting at those memory locations.
Deleting vs. Overwriting
The data a phone stores in a particular location will remain intact until it writes new data to those memory locations. As it writes new data to a location, the old data beneath it is destroyed. Files like text messages span multiple memory addresses, so a phone could write new data to some of those addresses and not others. This leaves parts of the deleted text intact. Some phones also have file systems with journaling features, so they can have multiple copies of the file at different memory locations. Unless every copy is overwritten, the text's raw data remains.
Digital forensic experts can recover "deleted" text messages from phones by scanning the raw contents of the device's memory. If a text message hasn't been overwritten, then the expert can recover the text in full. If the message was partially overwritten with new data, experts can still recover those parts of the message and possibly reconstruct the entire message. Even if you do a factory restore of your phone, your old text messages won't necessarily be overwritten.
Concerns over the privacy, and complete destruction, of data like text messages have led some smartphone owners to start using apps that secure the texting process. These apps, such as TigerText, Wickr and Privatext ,offer features such as text message encryption between users and the secure deletion of the text messages you send through them. Secure deletion means overwriting the texts' raw data to prevent recovery.