Until recently, the whole family had N900.
After having set up a Sfos Xperia XA2 for myself, I propagate to others.
I was searching a way to disable wifi and bluetooth for my sons phone as I don't really know how to avoid internet craps...
I don't know if Sfos allows internet via BT though...

Maybe, this can save some time to others with the same question.
Or maybe, it is totally herretic to do so

In /usr/lib/systemd/system/wifisetup.service, I commented out the line
And in /usr/lib/systemd/system/bluetooth.service, I commented the line
Take care,

The answer I couldn't find:

How to use gprs data for MMS only, without surfing ability?

Thanks, cheers,

Under Settings - Mobile network there are two access points.
One for Data.
One for MMS.

It should work as you wish when you modify the Data access point to invalid settings (but not tested and not verified, please comment back).

Situations (it's in the Jolla store) comes to mind. It's very powerful (takes a while to get used to its logic & interface though).

@peterleinchen: Ok, thanks. Have to find if I can make this read only.
Trying to grep the provider name through the filesystem to locate where the settings are stored....

@nonsuch: Great app. But it asks to install a module from untrusted source. Are untrusted sources trustable?

IIRC the developer has something to say about this. Maybe check out his website?

Well, you are right. Lazyness...

I understood that:
Sonar runs in background as root. It "has a basic client process executable name check to prevent just about anyone to acess the data..."
If Situations is uninstalled and Sonar left in place, someone else (an app) called Situations could exploit Sonar "rootness".

I concluded that:
Well, who TF (else than goopple) would hack my phone? Who has interest to me? I do no banking or money thinks on my phone.
I personally see no big risk.
I don't trust trusts more than untrustable sources where sometimes genious is born of. or?

I never had a problem running Situations, and it doesn't feel unsafe to me. That's not a qualified opinion obviously.
There's a Situations thread here on TMO, maybe this has been discussed?

edit: https://pastillilabs.com/sonar/
Indeed, sonar is very powerful and therefore potentially dangerous.
As you already said, you should take care to uninstall sonar before uninstalling Situations.

But here's another advantage of using a phone OS which such a limited user base: who in their right mind would bother to even try to exploit this?

After some weeks of use, I can confirm, Situations + sonar work great.
Clever and elegant application!