How exactly do i copy an iphone 3gs raw disk image to my computer?

A new phone with lots of valuable content was connected for the first time to a computer running itunes. A previous phone had been synced there before. For whatever reason itunes replaced everything on the new phone with the old phone. It did not make a backup.
I’ve jailbroken the phone and installed ssh (i think) but can’t seem to figure it out past this point. Is this the right approached to attempting a recovery of some of the data?