so, I've got a rooted Samsung G800F.

My objective:

• The phone has access to mobile data (not WiFi). (Intended for streaming Amazon and Youtube and maybe a bit of surfing or tethering.)
• The phone can not be called. Ideally the phone can not call or get/send sms and install other applications.
• The calls do not get blocked. (They are intended for a second cell using the same number/contract.)

What I tried so far and deem useless:

• Call Barring (My operator does not support this.)
• Call Blocking (My other phone has no chance to answer the calls.)
• Do not disturb/silent mode (It could still be answered and the calls are still visually signalled.)

What I'm trying now: Fiddling around with the phone app.

And here I'm absolutely lost and hope you can lend me a helping hand.

So, I tried Titanium, but couldn't identify the correct app. I froze and killed some suspiciously sounding/looking ones, but calls still went through and the ringer went uninterrupted.

Next I installed "Root Uninstaller" Here I found com.android.phone and had some partial success with killing this or some services.

There are two problems though:

1. I do not know what I'm doing. Not a clue. So, can you tell me what service to disable?
2. When I reboot the device it has problems and constantly displays an error message/is almost unusable.
3. (Falling under the "ideally"-category: can I just freeze some "Play"-App to prevent installation of messengers - relying on the phone number - and such?)

(Just FYI: I'm from Europe and might read and respond at odd-seeming times. I wanted to include the tag call-barring, feel free to add this.)