This is an easy way to backup your sms before flash your phone or save important texts stored on the sms.

I will use the P2kToolsVS

After you have been connected your phone, press the refresh button to start reading all the phone files.

if you see the image you will see the folder called msgdb. You need to backup ALL the files inside that folder.

Once the files are saved in your hard drive, you are able to flash your phone with a new firmware.

Too upload your sms backup to your new firmware, just do the same with P2k Tools and go to the msgdb folder and first delete all the files inside the folder, then you can upload your backup, and it's done.

I have tested and it works on any firmware!