When a text message is deleted from a Nokia phone it is not actually removed completely from the memory, it is simply turned off. Until the memory slot that it resides in is overwritten by another text message it is still recoverable. You just need a data recovery tool that can extract the text messages from your phone and turn the deleted messages back on so that they are readable.
Buy a SIM Card data tool. You can purchase these from online spy tool companies such as BrickHouse Security, Dekart.com and RecoverSMS.co.uk. As of 2010 these devices cost between £22 to £44 and include a software program to read the messages as well.
Turn your computer on and place the software that came with your kit into the CD ROM. The installation wizard will give you directions on how to install the program. Follow the directions and reboot the computer once it is finished.
Turn your Nokia phone off and take out the battery. Lift up the metal gate underneath it and take out the SIM card. Insert the SIM card into the text recovery device and connect the device to the USB port on your computer.
Click on the "Start Menu" and open up the software application that you installed earlier. Go to "File" and "Download text messages." A window will open and you will see a list of e-mails appear. The deleted ones will be in red. Undelete these by right-clicking on them and select "Undelete." You can now read the deleted text messages on your Nokia cell phone.