Are you going to format you memory card, but you want to backup your massages ? Here is solution of your problem. Connect your mobile to PC via cable or card reader whatever method you are using. Unhide files from folder option because these files are usually hidden. Now open memory card drive where You will see folders like SYS, PRIVATE, RESOURCE, DATA etc.The following screen shot show the Folders in MMC for better understanding.
Now navigate through PRIVATE folder. This folder contain “1000484b” and you will see mail2 folder (this is the folder where all our messages are stored)
copy “1000484b” folder and make a backup in your PC. After formatting your MMC again activate your mass media and copy the “1000484b” to the same location and restart your mobile. Now all the messages are restored.