Well if their phone is a blackberry or other java-based operating system, then deleted texts are GONE. Believe you me I have tried and tried and tried.
Some carriers with Blackberry will have options within the OS to "save texts to SIM card". Verizon does NOT have this option.
So basically, if your carrier supports this option, the OS will copy the SMS to the SIM card, which can then be read very easily.
There are PROFESSIONAL services out there than MIGHT be able to do it. There is also another way to do it by doing a full dump of the phone OS and memory space. Then, you need software to be able to parse and read the binary and hex codes. I am a computer expert, and I still have trouble with this.
Now I have recovered PICTURES taken by the BB camera. Since the mediacard can be read by Windows, then recovery software can find the JPEGS no problem.
See, the way most OS work when the "delete" a file is to just remove the index location of the file so the OS no longer sees it and thinks its gone. Then over time, the space where it is written is eventually overwritten with new data.
BUT UNTIL THAT TIME, the file can be recovered. I have recovered pictures more than 6 months old in the same session that I recovered the naughty pictures my wife sent another man.
Me - 32 Her -30 Married - 7 Years Together - 9 Years No Kids 05/21 - Bomb 6/8 - Exposed 7/9 - Re-Exposed 06/11 - She Filed