[CRImier]

The battery life is still unoptimized - I haven't even played with CPU clock scaling, WiFi is always on and its power management is at default settings, and there are a couple more things I can do that'll improve battery life (like, putting GSM modem in low power mode and adapting my GSM code to work with it). Right now, it lives for about 20 hours from a 4000mAh battery - playing music all the time, WiFi connected to something, with SSH open on my laptop. I just put it on a charger overnight, and like that, its uptime is 6 days now - if I ever forget to charge the batteries, I can just use spares to get through another day =)

[aphextron]

Did you ever consider an e-ink display? Are displays even a big power draw from mobile or is it mostly cpu/wifi/GSM?

My ideal phone would be iPhone 5 form factor with an e-ink display running FreeBSD with nothing but calling, SMS, a text based browser, and a terminal. Minimize absolutely everything and jam a 6000maH battery in there.

[CRImier]

The display is an OLED, and its power draw is kinda negligible - so the worst offenders are still CPU, WiFi and GSM. I'm going to add an E-Ink display someday - mostly for experimentation, as hardware upgrades like this will require somebody developing and maintaining the softwaree, but it could very well be a really good addon.

As for "your ideal phone" - something similar might just be my next year's project, though sourcing the parts will be hard, for sure =)

[squarefoot]

You may want to consider for future development other boards such as the NanoPI Neo Air and other similar H2/3 based boards. Availability aside, some folks at Armbian forums have done experiments with cpu throttling and the results are very promising: H2 and H3 CPU are a lot faster than the BCM in the RPI but can be optimized to draw less power. If you get one of these boards, don't use the images at the manufacturers site but go straight to Armbian where they host highly optimized images for most known boards.

[CRImier]

Each time ZeroPhone comes up on HackerNews, I learn something new that helps me go on =) Thank you, will be researching it when I'll be working "alternatives to Pi" topic =)