I still use my trusty flip phone from 2003 and do not own a smart phone. However, I found this little project interesting. If my washing machine surviving flip phone ever dies, I might consider this ZeroPhone as a replacement. The biggest drawback for me, though, is how thick the phone is when the battery is mounted. Regardless, I like the concept and its $50 in parts.

https://hackaday.io/project/19035-zerophone-a … y-pi-smartphone

Another interesting one is this world's smallest phone kickstarter,
https://www.kickstarter.com/projects/15009161 … iny%20dumbphone