Well, look at that! Yes, that's basically what I meant. Interesting.
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I didn't expect that it have been discussed before but theres really a possibility on having this kind of cold storage but I guess it wont really be created for sure because there are already lots of hardware/cold storages out there and I'm not sure if theres someone would pursue to create such project knowing that all mobile phones on these days do have all the accessibility on network which means you would really compromise your wallet informations but as being said you can restrict those permissions.
Well, at this point, there ae so many different ways to store your Bitcoin, that it implies, that there is no "perfect" way, but different ways with different advantages and disadvantages. Users may choose their preferred method based on their using habits.
Old smartphone is a very risky way to store your money due to high probability of breakage
Well, to an extend, this is true for every electronic device. While an old smartphone is maybe more probable to break at some point (although the sheer fact that it survived so many years may imply the opposite, actually), a Trezor, Ledger Nano or HDD can break just as well. Hardware wallets acknowledge this and use seed phrases. For smartphones, the same would be true: When you create a new wallet, you get a seed that you have to write down.
Now, the advantages a sartphone hardware wallet has over other solutions are:
Over regular smartphones and computers: If you are able to physically disconnect any broadcasting means, the only ways of inputting data would be by hand (typing), by camera (QR codes and the like) and by audio. Both typing and scanning QR codes are a) highly observable ways of inter-device communication, as well as b) extremely slow, thus greatly decreasing the risk of implementing malware on the smartphone wallet, as well as performing man-in-the-middle attacks.
Audio is a little more tricky, but maybe just ripping out the microphone might do the trick
Over paperwallets: Other than with pure paperwallets, consisting either of seed phrases or privkey QR codes, with a smatphone wallet, you are still able to generate transactions, on a device, which is essentially airgapped.
To get the transaction from the device into the "real world", I'd suggest communicationg it to another smartphone, using the screen of the smartphone wallet and the camera of the broadcasting smartphone. I won't go into detail here, but again, you have a way of output, which is provingly one-directional and highly observable, preventing, once again, spying and man-in-the-middle-attacks.
Over hardware wallets: Well, not so much, actually. Unless you're a tinfoil hat and mistrust anything you didn't build with your own two hands and which comes from some private companies, which may very well have put in some weak random number creators to guess you keys or whatever (disclaimer: I personally don't believe anything in that direction, but some people might.), a hardware wallet will probably do its job just fine. I don't know, maybe I'm missing something, though…
Enough rambling for today.
