Hello, Data protection is through encryption, which is fairly normal, and through physical isolation, which is less common. Basically the cellular network and the data are held at arms length, and there is no path from the cellular network to access user data without the user's active participation.
Environmental sustainability is difficult to measure, but here are the things that we have done to make the device much more sustainable, focusing primarily on extending the lifespan of the phone (and thus answering your final question as well).
1. By being larger, the device requires less miniaturisation, which in turn means less need for rare earth metals etc that are typically used to make high-performance tiny components. Indeed, the entire device is less tightly integrated, which means that it is possible to replace each major component, thus also allowing a phone to be maintained at reasonable cost over many years. The physical device will be designed to last many years.
2. The large battery means that even as the battery capacity decays over a number of years, it will remain more than sufficient. Should the battery ever require replacement, it is a straight-forward process to do so.
3. By including a solar panel, the device is able to self-power, which partly supports battery life for extended device lifespan as the battery naturally ages, but also allowing it to operate on its own renewable energy supply.
4. By abandoning the race to keep up with the latest advances in computer processors the key driver for replacement of phones every year is removed. That is, by focussing on high-performance software instead of high-performance hardware, the need to upgrade the hardware on a regular basis is removed.
5. Unlike practically every other phone out there, it is possible to upgrade and replace the cellular modem part of it as required. That is, while the phone may ship with a 3G or 4G modem, it will be possible to upgrade to 5G when available, or even just to "side-grade" to a modem that operates on different frequencies, in case you move countries, or your cellular network changes frequencies, or you switch to a carrier with a different cellular network technology. Data storage is on microSD card, which is similarly upgradeable.
Now, in terms of expected lifespan, I would hope for a minimum of five years of serviceable use, although much longer is possible.
While there are some similarities, our approach is quite different in that we are purposely aiming to create a simple phone that is completely open in terms of hardware and software architecture. So while it might boot super fast like the low-end Nokia phones, you will be able to install (and indeed write) apps for it, for example.