Help with a unique iPhone problem

Or maybe not so unique.

I've searched for answers to this and the only threads I can find on any site are from 2010 so I'm hoping something's changed since then.

Here's the Cliffs Notes version of my story:

I've got a 3GS, backed it up regularly to my computer, which I in turn backed up regularly to an external hard drive. Computer crashes, I don't have money to buy a new computer so I just use my iPhone and iPad. Last August, my jailbroken iPhone crashes while on vacation and I use my friend's computer to restore it to factory settings, losing everything - except in the back of my head, I know there's a backup of my phone sitting on my external HD and that I can figure out how to go about restoring it when I get home. Well, weeks turn into months and I end up not restoring it from the backup and now I have a years worth of texts, emails, and photos on my phone.

With the new phone coming out, is there anyway to merge the two backups so I can take everything off of the original backup and then everything off my current phone and put them onto my new iPhone next month? Really all I care about are the text messages and photos. Like I said I've googled this every way I can think of, but the most recent search results are all from 2010 for some reason.

Thanks for any and all help!