For more than 19 years, every GSM mobile phone is running a proprietary
protocol stack on a proprietary operating system on top of equally
proprietary hardware.  Billions of phones have been shipped worldwide,
running as a black box controlled by the phone maker and/or operator -
outside the control of the user

Most of those devices have no user-upgradable firmware for the baseband
processor, and yet those billions of GSM phones are all connected to a public
network.  Their software is complex compiled C code on a CPU without any
form of memory protection.

Mobile phones have all sort of features that the user would never want. Why
would he want his phone to reveal its GPS position to the operator?  Why
would he allow the operator to hide from him, if calls are not encrypted?

The only solution is a Free Software / Open Source GSM baseband stack.

OsmocomBB has set out to create this protocol stack.