Since I'm more likely to remember this .stack than the url of the blog-page... here's for future reference. Some good comments in there.

hackaday.com/2015/09/10/want-a-low-cost-arm-platform-grab-a-prepaid-android-phone/

$19.99 phone... and if I understand correctly, you can cancel the $19.99/mo service at any time and still receive a limited amount of *free* data (and voice) from there-on. IoT with UI and more. 

Looking a little bit more into things, it seems there's in fact a means for running Debian or others on phones, including gcc, X, etc. So, hardware-wise, probably not well-documented, but definitely a powerful processor, decent screen, bluetooth, WiFi (and even free 4G?). USB-OTG for your AVR-programmer, FT2232H-JTAGger or whatever...

 I think it's plausible, but not certain about the driver-side of things (most of the Linux-on-phone methods I've found thus-far run 'chroot' alongside Android, so would rely on the android's kernel's available drivers... right?)

https://www.freedompop.com/offer/samvictory19pp?utm_source=facebook&utm_medium=cpc&utm_campaign=Samsung-Victory:samvictory19pp&utm_term=LG:NFD:Lookalike+(US+1%)+-+phone+subs_24APR15:2099:Men&utm_content=Victory-1-NF:Victory-1

And of course battery and charger ;)

how about if we just connect the uC with the phone via some dedicated link, BLE most probably and use some all controlling app custom made which runs directly over the android OS so no driver issues.

See choice 3 of my LONG comment below.

I'm definitely keeping this all in the Plausible Tools list... Dunno much about Android, myself. Actually the driver-issue is kinda absurd, why run a programming-dongle off the phone? Makes more sense to use USB-HID or USB-CDC(? RS-232) which are surely already supported. Or bluetooth, or whatnot. Only problem with this phone is it doesn't *supply* power on its OTG port...

The way I see it, there are a few options that can be considered.

1) Design and make a complete phone from scratch or from using some half-done design (I hear they are available in China - if you have enough volume) - this could result in something like the C.H.I.P. computer - partnership with some manufacturer - would require lots of work on both HW and SW side - but will be the IDEAL thing - but the technology will get obsolete quickly as phones upgrade much faster. Can get as many made as demand, but can only get em made if demand is HIGH enough


2) Choose an already available phone and start work on it, try to select a model which is most documented from HW perspective and then work on the SW, will need some reverse engineering as not a single phone is open source (AFAIK) - HW will become obsolete even quicker. cant get em made when the manufacturer stops making em.

3) Work on making a custom ROM for Android, like CM (Cyanogen Mod) is. It will be able to run normal APKs and the ROM should provide customization from a hacker perspective - phone disable/enable - boot-up application selection - application lock (allow only a few apps to be run) - Write apps which take over every HW related task from the Android and implements em as the user likes - would be cost-effective as compared to the above 2 options - I think Android already provides the ability for apps to take over things like SMS, Phone Calls, Wifi, bluetooth etc.

4) .... I gotta go, but there maybe other options.


So far, I think option 3 or some variant of it seems the best possible option, only issue will be that anyone who would want to use it will need to learn how to make APKs for Android and that is a BIG hassle, maybe a framework or some good and easy to use API could be made for the newcomers.

Example: I have an old/cheap Android phone, Moto Droid, I install the ROM on it - or the APK if the solution consists only of the app. The app takes over all Calls, SMS, connectivity functionalities and somehow lockss the phone to always run that app on boot and NOT allow to close the app. Now I can program the app to communicate over Bluetooh/Wifi with an AVR/Arduino/other Embedded System as the interface to the World and the phone provides the processing power and the human interface as needed.

you can install gcc and binutils and make better than android without driver issue

A Linux distribution for arm, (widely used in mobile phones processors) like Raspbian gender should be enough to take control of most devices with an Arm processor. (Android and company)
One problem is to list all the embedded hardware specific to each manufacturer to implement adequate free drivers. (gyroscope, various sensors, etc ...)
The other problem is to take control of the processor during initialization of the device to install this Linux.
I already thought (some) to this type of hack, the problem is to disable the internal Bios Rom during initialization.
If someone has an idea to make this quite feasible manipulation to ordinary mortals that we are, I'm interested.

I can understand driver issues and such... but cant do anything much about it myself.

Yeah this is a pretty cool idea, would be a great way to recycle old smartphones for useful applications and reduce ewaste something we all can get behind! I don't know anything about android dev or hacking but I still think it would be cool if this happened.