I mean I would have root access, so thats a start I guess.
Yup they are like LInux Kernels when you have root access you can lots of stuff ,like manipulating the apps the lower level settings like the internet connection by accessing and editing the interfaces file under networks etc!
Its like the security shell for the linux system and one windows have to which is rather poor in earlier versions of windows like XP so messing with the core settings require getting deep.
I use Embedded Linux on a SBC . Its a Ubuntu!
I would suggest buying a BBBlack or a RaspI or anyother good for starting SBC rather than hacking an iPhone clearly this isn't a start plus it will have a lot of limitations like working with diddling closed iOS and getting enough GPIOs to do your shit!