Can I access the filesystem of an android device? I have an android device that doesn't start because it tries to activate carrier's network.  Its out-of-contact CDMA mobile which was ported to another carrier. I accidently did a reset and after that it awlays tried to activate carrier. 

Currently when I connect it, I can see it as MTP Device, but I don't see the filesystem. Is it possible for me to go to the filesystem directly and remove possible apk's that cause this?

I am thinking of chroot-ing or something similar into the system and remove all the stuff that could trigger this activation. Do I need to use ADB shell or to connect to the device?
To get access to the filesystem you need to be rooted and you need to use ADB. MTP is way to limited for the low level access your needing.