I came across this while I was surfing through a forum. I don't know if it was available before, but or me, this is the first time I come across it.
Credits go to yogeesharma (I don't know if this has been posted on another forum by someone else so credits to this original poster too).
This is a solution for backing up and restoring messages that are stored on the SD card.
1 - Connect your handset to pc in the “Data transfer” (Mass storage) mode
2 - Go to the Private folder on your memory card (of course after having set your pc to show hidden files & folders)
3 - Open the "1000484b" folder (or any folder with a "Mail" or "mail2" folder inside)
4 - Copy the "1000484b" folder to your PC
5 - After you format the SD, copy back the folder from the pc under E > Private using mass storage mode.
6 - That's it.
Of course this functions only for messages saved within the memory card, so messages saved on the phone memory won't be transfered. We're still waiting for a solution for accessing the private and sis files on the phone memory, I guess we'll keep waiting. In the meantime, suit yourself with this little help.