You are not likely going to be able to destroy or unplug all the pieces of hardware you need and still have a functioning iPhone. It will likely simply not work. Not to mention some of the components are likely embedded in other components. I think I remember some phone models had Wi-Fi and or Bluetooth integrated in the processor chip.
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I think he doesn't need to disassemble the unit just to destroy the Bluetooth and WiFi. There's alternative for this without touching any hardware components.
If he knows how to jailbreak(with checkra1) the unit and is able to switch it to diag mode or purple screen, he can replace the MAC address of both Bluetooth and WiFi by editing the Syscfg, where you can find both Wmac and Bmac, to destroy it or make it unable to use; just replace the MAC with zeros and save.
If you jailbreak your iPhone, root your Android or use a Linux terminal with out knowing what you are doing then you are better off not complicating things at all and using a default Operating System instead with no tricks at all. Security wise, I am pretty sure this actually LOWERS your phone security than improving it in any way! And considering OP is looking to turn it in to a Hardware Wallet, I would definitely not suggest doing this.
Does OP really need a portable device that small? There are older laptops they can buy and take all the wireless chips out of manually with out having to struggle at all. Modern portable devices, even laptops, are a PAIN in the back to modify now!
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Its not like I would encourage using a device like this (whose main function is to communicate with the outside world) to be "air gapped", there are much easier, smarter alternatives out there like hardware wallets, but hey that is an interesting idea so I did a little look around online, and you might be surprised to learn that there are actually bags that completely block all signals. Faraday Defense make ones, for example. These have up to three layers of RF shielding fabric and work via the "Faraday cage principle". Apparently, they are handy if you dont want your phone to be tracked. So, if anyone is worried about that for example, this apparently does the job.
A Faraday cage is as useful as the other suggestion about aluminium in this situation. In fact. Considering most people do not have the budget to pay for a high quality Faraday bag, I would rather recommend using aluminium foil instead because cheap Faraday bags will most likely NOT isolate the phone.