Perhaps this is already known, but I just found out about it today, and I didn't see any other topics about it:

The Jolla Phone, Jolla 1 or whatever you want to call it, will no longer receive new software updates. 3.4.0.24 is therefore the final version of Sailfish OS for the Jolla Phone.

The reasons are basically just that it keeps getting harder to update all of the different software components due to its really old Linux kernel, which is coincidentally also stuck at version 3.4.

Although I completely understand the reasoning behind this decision and would even make the same decision if I were in Jolla's place, it does mean that I'll have to start looking for a replacement for this brilliant little device, which has been serving as my one and only phone for seven years. The paint has chipped off in many places, the battery holds less than 70% of its original charge, five years ago the loudspeaker broke but a month later it magically repaired itself and hasn't malfunctioned since, the SIM card reader is now occasionally starting to lose connection to the SIM card, TOHKBD2 barely works anymore and has turned into an odd fridge decoration, SolarTOH never really worked in the first place though I still attached it every summer, at least 90% of modern Android software is no longer compatible, and it feels like the camera takes grainier pictures by the day. Once, my Jolla Phone was accidentally catapulted across an entire room and came out unscathed. For seven years, I've been able to boast about it still receiving all of the latest updates where other phones are already unsupported before they reach the stores. This monumental embodiment of true innovation kickstarted it all.

So long, Jolla Phone, and thanks for all the fish.

You can read Jolla's official blog about it here: https://blog.jolla.com/jolla7/

My original Jolla phone endured swimming in toilet, and sleeping 2 months under snow that variated between wet and hard. And it came out unscathed. What a trooper.

Amen. 10 chars.

Hope now you can install Linux on them :-)
I got Wayland (Weston) running on my N900 with GLES2 in tow!

Is that last version best or should I upgrade from factory version to some else?

It has a browser engine that's at least somewhat usable and has the highest compatibility with applications and patches. There's really no good reason to install an older version on purpose.

Directly to the point : whats the chances for Jolla to provide
kernel sources to the community? Id love to see a more recent kernel on the phone!

I think it is all there at https://git.sailfishos.org or in Jolla's source archives (https://releases.sailfishos.org/sources/), as well as the original Qualcomm ("CodeAurora") kernels for Android (see e.g. https://wiki.codeaurora.org/xwiki/bin/QAEP/), Jolla's kernel and adaptation is based on.

Well AFAIR there is one slightly newer, but for the binary modules to fit (which you cannot recompile), it still has to be and is 3.4.x.

The problem is exactly like @olf nails it; usually having kernel sources is not the glitch but the proprietary modules is.

There are ways around it, one can write wrappers for the proprietary bits and hence get as recent kernel as one desires but it is quite tedious and creates a maintanance hell.
(but yes, doable if you desperately need a once-off solution)

If you decide to go that way, be prepared to write quite a lot of support code against glibc...

Oh trust me, these are not the problems I am looking for

But wondering, blobs being radio / camera etc?

I guess wrapping only takes you that far, considering how usually kernel modules share different declarations in shared header files etcetcetc.

Perhaps what is surprising is;
being the phone a SoC, and being qualcomm the producer / owner, youd expect them to be able to opensource all the components.