Default [Q] Sending AT commands to radio

Hey fellow modders!

I am currently trying to send standardized AT commands to the radio unit of my rooted Samsung Galaxy S2 Plus (I9105P). I am running a customized version of the Samsung stock ROM on the device. The customization of the ROM was done with the Android Kitchen.
Every time when I try to send the commands via microcom (as root of course) to various devices in the /dev/ directory, I get no response at all. Am I wrong in thinking that this should actually not be device specific? In my understanding there should be a standard (Linux-like) way.
First of all, I need to find out which device exactly is the radio unit. It would be great if anyone could give me a hint.
Then I need to know, what I should do to send AT commands (such as CPIN) to the device. Maybe there are some special parameters that have to be passed to microcom?
I have already tried the following approaches:

[TESTING] Fun with the radio
at commands
How to talk to the Modem with AT commands

Looking forward to any help you can give me.