Dear Måns ,
yes, libgsm available as package in many distributions, typically at the current version of 1.0.19:
If a local copy is kept within sox, it should probably be updated ...
As
a small sign of being interested in keeping the cmake build system for
SoX, a patch for CMakeLists.txt is attached, which allows detection of
gsm.h, when it is directly in the include folder in addition to
detecting gsm/gsm.h so far.
The patch also includes a fix for detecting lame.h in addition to lame/lame.h
Best regards
Wolfgang