Yes Mitch, I did that but the Fax internal messages are printed by this line which has no knowledge of the session.
  switch_log_printf(SWITCH_CHANNEL_LOG, fs_log_level, "%s", msg);

I do not think, it can print the uuid without knowing the session ?

Here is a log snippet to show uuid prefixed at other places except line 286 of mod_spandsp_fax.c shown above

2012-03-27 13:40:38.604877 [DEBUG] mod_spandsp_fax.c:286 FLOW T.30   1... ....= Extension indicator: Set
2012-03-27 13:40:38.604877 [DEBUG] mod_spandsp_fax.c:286 FLOW T.30   .... ..0.= Compressed/uncompressed mode: Compressed
2012-03-27 13:40:38.604877 [DEBUG] mod_spandsp_fax.c:286 FLOW T.30   .... .1..= Error correction mode (ECM): ECM
2012-03-27 13:40:38.604877 [DEBUG] mod_spandsp_fax.c:286 FLOW T.30   .... 0...= Frame size: 256 octets
2012-03-27 13:40:38.604877 [DEBUG] mod_spandsp_fax.c:286 FLOW T.30   .1.. ....= T.6 coding: Set
2012-03-27 13:40:38.604877 [DEBUG] mod_spandsp_fax.c:286 FLOW T.30   0... ....= Extension indicator: Not set
2012-03-27 13:40:38.604877 [DEBUG] mod_spandsp_fax.c:286 FLOW T.30 Selected compression T.6 (3)
46736448-77e4-11e1-855c-b3286880c45b 2012-03-27 13:40:38.604877 [DEBUG] mod_spandsp_fax.c:327 === Negotiation Result =======================================================
46736448-77e4-11e1-855c-b3286880c45b 2012-03-27 13:40:38.604877 [DEBUG] mod_spandsp_fax.c:328 Remote station id:
46736448-77e4-11e1-855c-b3286880c45b 2012-03-27 13:40:38.604877 [DEBUG] mod_spandsp_fax.c:329 Local station id:  Sangoma Fax Ident
46736448-77e4-11e1-855c-b3286880c45b 2012-03-27 13:40:38.604877 [DEBUG] mod_spandsp_fax.c:330 Transfer Rate:     4800
46736448-77e4-11e1-855c-b3286880c45b 2012-03-27 13:40:38.604877 [DEBUG] mod_spandsp_fax.c:332 ECM status         on
46736448-77e4-11e1-855c-b3286880c45b 2012-03-27 13:40:38.604877 [DEBUG] mod_spandsp_fax.c:333 remote country:
46736448-77e4-11e1-855c-b3286880c45b 2012-03-27 13:40:38.604877 [DEBUG] mod_spandsp_fax.c:334 remote vendor:
46736448-77e4-11e1-855c-b3286880c45b 2012-03-27 13:40:38.604877 [DEBUG] mod_spandsp_fax.c:335 remote model:
46736448-77e4-11e1-855c-b3286880c45b 2012-03-27 13:40:38.604877 [DEBUG] mod_spandsp_fax.c:337 =========================================================================


regards,
Anita