Recently I put together my dissertation (and subsequent website) on how to retrieve deleted text messages on the latest mobile phone handsets. Because this technology is going to continue to expand as phones change and new hacks are created to scan the phone better - I thought I'd put together a wiki for it (as part of my grade as well!)
So what happens when you delete a text message on your handset? Turns out it's similar to deleting a file on your computer. To save processing power, battery life and time the data isn't so much deleted as just forgotten.
Rather than writing over the memory location holding the text message your phone just kind of forgets it's there. The data isn't shown on your SMS app and the memory is free to be used again and be overwritten. From a development point of view this makes a lot of sense and it's how most systems work (not that popularity means it's right).
Keeping Deleted Text Messages
If you accidentally deleted something or your phone breaks and wipes everything then this works in your favour. If you were relying on your deleted text to stay deleted for privacy? Then not so much.
Once the memory has been used again there's no bringing that message back. So if you're specifically looking for your messages to stay deleted you can find apps which take the time to overwrite the unused memory locations. I'd have it run in batches at 3AM though that's not something you'll want to always have running on your battery won't last long.
Your message is also more likely to not be recovered over time. The more you use the handset the more chance that part of the memory is going to be used which means a lower chance of it being recovered. However, there is anecdotal evidence to say that messages have been recovered from a smart phone 10 years later. But it does depend on various factors such as the available memory on the phone (higher with the more recent iPhones etc…) and how much it's been used.
Recovering Deleted Messages
While there are companies styling themselves as mobile forensics labs and computer shops across the world offering to retrieve deleted text messages for a fee - there's really no tech knowledge required these days.
Not to say there's no tech skill required for developers. Software to do this has to be able to access the recess of a phone models memory, scan and find the footprint of deleted data, as well as the data itself and recover it to the phone. And ideally it has to do this without touching the memory as much as possible to retain the integrity of the data hiding in there.
But developers have done just that and it's a push button solution for free software now. Connect your phone by USB and hit go. That's if you have a newer model so namely an iPhone, Android, BlackBerry or Windows phone. I won't suggest specific software just in case this wiki does go out of date (not that it should, this is unlikely to change for a while and I have more updates coming) but if you just search for recovering messages on your specific OS so, for example, iOS or Android there are plenty of free tools around.
If you're using an older handset then your OS is unlikely to be supported. The software needs to be able to access the memory and know the footprint to look for so it won't just work on any phone. Your remaining options in that case would be accessing the memory on your phone via USB and a file viewer and looking manually (bring pain killers for that headache) or the SIM card.
If your phone is storing messages on the SIM as older phones do (and newer phones can, but generally don't) then you can get a SIM card reader for a few bucks and recover the texts from the SIM in the same way as we would from the memory. The main difference is the SIM memory is very limited so you have less chance of success.
The latest phone models statistically have more memory. This means that there's a better chance of being able to recover deleted text messages from the memory. But the increased processing power and RAM would mean that phones could handle overwriting memory instead of ignoring it if developers wanted to move in that direction for privacy. Maybe offer that as an option for the handset, but for the moment messages are pretty easy to recover regardless of tech skill.