There are linux based operating systems beside android..so you get your linux system...you pay your programmers to.progrsm for that only and bypass bill gates or google creeps or iphone robber barons. You never have to worry bout their unnecessary updates...a decent generic cellphone could be about 30 bucks wholesale....
The stupidest decision is to reinvent the wheel when there are perfectly good wheels already out there that will do the jobs you need done at a reasonable price where you have recourse if it doesn't work right. Doing things yourself when there are already ready made solutions never turns out to be the least expensive or the best answer. . . see Cheop's Law as a reference of just one of the pitfalls awaiting people who think they can do it better than the free market can and save money.
First of all is the fallacy that there is a "decent generic cellphone" which can be had for $30. You get what you pay for, and support is one of those things. . . as is quality.