Seems like that would put that saved data back on the phone.1 backup
2 erase all content and settings
3 setup as new
4 restore from backup
- Make a backup in iTunes
- open iBackupBot
- go to the relevant backup
- hit Other Multimedia Files (you might have to click on the tab afterwards, in case it goes straight to camera roll instead)
- sort by filename by clicking the Filename tab
- go to MediaDomain/Library/SMS/Attachments and highlight all of them.
Now you can delete them all by right-clicking and choosing delete (you might want to export them first, up to you), close iBackupBot and restore to backup in iTunes.
Tadaa! Space recovered, texts/SMS/messages (whatever you call them) still there!