Hello,
Regarding questions how to use the ETSI codec: It consists of two steps, "cdecoder" and "sdecoder". The ouput of "sdecoder" is raw sound in signed 16-Bit PCM format with 8000 samples/second. For example Audacity can play it without problems.
(And no, its no "magic", it just requires to read a few comment lines in the source code of the codec).
Best regards, Dieter