I had thought ADB was the only way to unlock.
I have found in the wild US At&t phones with a bootloader only unlockable with an app and code form At&t after verifying the phone has been paid off 100% by the subscriber while they are still under contract.

Re: Ubuntu Touch above, I tried it out early with my Nexus 7 flo but found it to be pretty limited, I place privacy, real GNU Linux, and function on a balance and try to get the best of all 3. Pretty much until there are used Purism or something similar phones available I am in a tough spot for hardware as I think most of us are.

That just might never happen.

Ooof!
Yea I know a guy years back who was always doing a hybrid confidence scam/tech accumulator business. He printed stock and traded it for cash, it was unbelievable how many years he lived well for running that scam.
Seriously, if you are producing in Senzjen where they can whip up a prototype in weeks why has nobody ever found a way to get a FOSS phone made. I bet it could be done between $10k-$100k especially if you walked in with gerbers or kicads ready to go.
(Yes I know you need to go through prototyping phases to test out the system especially the RF components)

To illustrate the idea of custom design just look ath those old real-fake N900s with DVB-T and could play J2ME games years ago. The thing is I feel like most of this Chinese stuff is a dirty cheap hack both hardware and software made in some dirty shop; it works, barely, no time for QC and falls apart like a house of cards if you try to do any normal hacking or customization over their fixes.

It's in the numbers apparently (something also mentioned in the article series I linked) - it's much harder to find someone willing to do relatively small batches.

I found an international model Samsung S4 mini LTE gt-19195 AKA serranoltexx.
It required the program heimdall available on the Ubuntu repos to get TWRP over the the S4 without needing to OEM unlock it.
While I was installing LineageOS 14 for microG I used the instructions from the LineageOS wiki on the S4 mini.
After I had TWRP loaded it was easy to adb sideload the LineageOS for microG zips and the supersu zip from LineageOS.
Just to be clear LineageOS for microG is a slight fork of regular LineageOS just with microG components pre-installed.
So far it seems to work great and I have a pocket sized web browser though the NFC doesn't seem to detect my transit card.
My big bump was trying to track down how to OEM unlock the phone in the Samsung GUI, the youtube ideas involved messing with the calendar settings; any good device should never require booting into a bad OS to load a good one, the S4 mini qualifies if you follow the heimdall a recovery and adb sideload your OS zip files.
The screen is beautiful and colorful but this phone(tablet to me) burns amp hours like a fiend when it is working hard, good thing it is mostly a bluetooth tether web browser to me.

Other notes:
The S4 mini requires a powered USB OTG cable to work or making a microUSB OTG adapter which shorts the wires to pins 4 and 5 of the usb port.
The NFC equipment unlike that of my Nexus 7 doesnt seem to talk to RFID objects like my transit card, too bad but not a fatal problem.

I now need to get some good schematics or at least chip datasheets(damn you companies who require NDAs for datasheets) and neuter the cellular capability. I could just cut RF traces but I would rather lift-and-cut pins fom an IC if I can. I just dont feel that this design with the cellular having direct lines to the CPU is acceptable.

Now to change it form a phone to a a tablet in software

lifted from here: credit to: Death Mask Salesman on Aug 18 '16
https://android.stackexchange.com/qu...out-a-sim-card

Sucessfully tested on my S4 mini I9195 running LineageOS 14 for microG which now ignores its cellular radio not wasting energy desperately pinging for a cell tower we don't want it to bother with. Unfortunately due to the desires of state and corporate entities to keep tabs on us using the excuse of easy tracking for emergency services it is no surprise the satellite navigation is implemented on the cellular radio's chipset.
Wifi - Works
Bluetooth - Works
Broadcast FM Radio RX - Works
GPS - Appears to be Disabled
Hall Sensor(compass) - works
Cellular telephony and data - Disabled and status hidden
The Phone is now working as a tablet for all practical purposes, the first command given below disables the cellular telephony and data the change persists through reboots. This small ex-phone is now well suited to occasional carry when needed as a small handy pocket sized web-tablet tethered to my N900 via bluetooth PAN.
I suspect the cellular modem may cycle through a up period and send pings during power on before the OS loads and begins to ignore the cellular hardware This mod will not make your I9195 invisible to the cellular system in a safe reliable way or reliably protect your privacy. I have not tested the second way that uses a script only the su -c "setprop persist.radio.noril 1" solution but I have tested undoing it; reboot and phone and GPS are returned. The disabled GPS can sometimes be a problem so I will probably switch to the radioon and radiooff scripts solution so I can have satellite navigation as an option when needed.
__________________________________________


From the Terminal
Disabling RIL

If the operation is not to be performed frequently, a single line of code will be all that is needed:

. This will make the phone ignore the Radio Interface Layer, thus ignoring the presence of the antenna. A reboot is required for the change to be in effect, and it will persist across reboots.

Plus, disabling RIL also makes the "No SIM Card icon vanish.
Enabling RIL

Enabling RIL again is just a matter of flags. As can be seen from the below example:
, the command is equivalent, save for a 0 instead of a 1. As before, a reboot is needed.
As a custom function
__________________________________________________

I've also devised two functions to be added to the /system/etc/mkshrc file. Of course, it's usually needed to remount the /system partition as read-write, but the procedure will not be covered in this answer. (FYI in lineageOS with root enabled Amaze(with root enabled) file explorer to move mkshrc over to Documents then edit it by mounting it over USB MTP on my Ubuntu laptop then sending the edited mkshrc to overwrite the copy in /system/etc. Despite this this added lines to the file /system/etc/mkshrc and rebooting radioon and radiooff commands is not working so far for me)

This file takes care of various environment variables and aliases to be loaded by the Terminal once it is started, so fiddling with it is often discouraged. We can, though, add our personal functions and customizations just before the line that reads:

: place customisations above this line

. I would like to remind that : is a special shell builtin, and thus must be left untouched.
Disabling RIL

Here, we'll define a custom function radiooff, which will next be callable from the Terminal at will. The code is as follows:
. I'd like to remind that it's vital to place this code at the bottom of the file, but above the line mentioned at the start of this section.
Enable RIL

This function, as the comments explain, is the inverse of the radiooff function:
. Upon saving the modifications, the functions radioon and radiooff will become available for use after the CyanogenMod Terminal application is started, or restarted. The procedure for using them is simply to enter the name of the needed function and enter.

It may be obvious, but the second solution will not work if the user uses a Terminal that is not CyanogenMod's.

(edit)
I am not too concerned with getting the radioon/off script working I have made a note in Documents with the noril command lines so if I need GPS or want to use it as a phone I have the tools to do so. If you figure it out leave a comment in the thread. I think I have what I needed when I began this exploration, I have a mostly FOSS mini tablet so I have a modern web browser while using my N900 as my primary phone. I want to leave everything I have tried as documentation for future users.