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.
Why does not wanting to have someone eaves drop on me mean I have to use inferior technology? I find that to be offense in the extreme. Everyone should be concerned about or more ideally not have to worry about people accessing their phone without their knowledge.
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.