This does seem feasible for the specific use case of a protected phone for "clandestine" meetings. My initial thought was they'd have to redesign it for every

This does seem feasible for the specific use case of a protected phone for "clandestine" meetings. My initial thought was they'd have to redesign it for every phone, but that's not necessarily the case. If eaves dropping is such a concern for you, I would think you would be okay with not having the latest gen phone. Or having an old one just for these sorts cases. I suppose the concern then shifts to whether this device is easily subverted, or whether it's easy to determine if it has been subverted.