Free trial version has been enough, but I'm considering buying the full soft, for it really worked
Basically, this soft si capable of scannig both your phone internal memory and any iTunes back-up on your computer (a Mac, in my case). It creates a whole SMS local back-up archive for you, adding SMS from any source you scan (no duplicastes are created in the local archive though), it's pretty neat and nicely sorted actually, then you can restore any SMS conversation or message to either a local iTunes back-up or directly to your iPhone.
I did both. First I restored my lost SMS conversation to my iTunes back-up, then -since I did not want to restore the whole iPhone from that- I restored the same SMS conversation directly to my phone. It took quite some time. It works, but it's slow. Be patient. Don't think the soft is going SNAFU, it's not. Don't panic. You have to wait. Plus, after the restoring process ended, the iPhone self-hard-rebooted itself. Matter of fact, it took so long (phone progress bar during start-up also included) that it may be the software actually created a local updated/edited back-up and then restored the whole phone from that all by itself, but alas: it worked.
What if you deleted some SMS and you *don't* have any local iTunes back-up for them to be retrieved?
Well, supposedly a soft called Wondershare Dr.Fone for iOS(http://www.wondershare.com/data-recovery/iphone-data-recovery.html) should be able to scan your phone for 'deleted yet not overwrited data". I tried that also (to recover some more still missing SMS), seems a good soft and all, but the process is quite invasive. I finally gave up in fear of damaging my phone. The whole process is described here:
And, if you manege to retrieve any 'deleted but not yet ereased data', you should be able to restore it in your phone witha companion software called: Wondershare MobileGo for iOS (http://www.wondershare.com/ios-manager/) should do the trick, but I havent checked with it.
As for mere SMS and *other data* back-up (not restoring) from iTunes back-up (not directly from he Phone), I also reccomend iBackupViewer - it really works, and it's free.