I made a header file here:
http://cncmods.net/files/libisi.h
for libisi and libisi-glib. It contains definitions of all libisi/libisi-glib functions that get called by things outside of libisi except for libisi_pipe_* (which I couldn't figure out and which are only used by csd-gprs)

I also found this online
http://pastie.org/pastes/1149648 put there by someone in the distant past (the stuff in that file helped me a LOT with reverse engineering of libisi) and I extracted the contents of that file as
http://cncmods.net/files/isi_info.h so people can use it
Its a complete header file for libphinfo0

Coming up next I will be posting header files for the various cellular modem interfaces (describing all the structures and stuff you use to talk to the cellular modem) along with some reverse engineering of liblas, location-daemon and location-proxy.

Small update to libisi.h added