I was executing freeswitch through screen and it seems debug output is controled by
freeswitch@sipzag> 2014-04-15 23:41:43.338539 [ALERT] switch_core_media.c:334 Looking for zrtp-hash
2014-04-15 23:41:43.338539 [ALERT] switch_core_media.c:289 Deciding whether to pass zrtp-hash between legs
2014-04-15 23:41:43.338539 [ALERT] switch_core_media.c:291 CF_ZRTP_PASSTHRU_REQ not set, so not propagating zrtp-hash
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2839 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC]
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2854 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC_COMPLETE]
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2839 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC]
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2854 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC_COMPLETE]
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2839 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC]
2014-04-15 23:41:43.338539 [ALERT] switch_ivr.c:1835 sofia/tone_detect/
xlite@129.sip.testy.com receive message [TRANSFER]
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2854 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC_COMPLETE]
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2839 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC]
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2854 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC_COMPLETE]
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2839 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC]
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2854 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC_COMPLETE]
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2839 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC]
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2854 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC_COMPLETE]
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2839 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC]
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2854 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC_COMPLETE]
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2693 sofia/tone_detect/
xlite@129.sip.testy.com receive message [PROGRESS]
2014-04-15 23:41:43.338539 [ALERT] switch_core_media.c:334 Looking for zrtp-hash
2014-04-15 23:41:43.338539 [ALERT] switch_core_media.c:289 Deciding whether to pass zrtp-hash between legs
2014-04-15 23:41:43.338539 [ALERT] switch_core_media.c:294 No partner channel found, so not propagating zrtp-hash
2014-04-15 23:41:43.338539 [ALERT] sofia_media.c:92 sofia/tone_detect/
xlite@129.sip.testy.com receive message [RING_EVENT]
2014-04-15 23:41:43.338539 [ALERT] switch_channel.c:3430 sofia/tone_detect/
xlite@129.sip.testy.com receive message [AUDIO_SYNC]
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2839 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC]
2014-04-15 23:41:43.338539 [ALERT] switch_core_session.c:2854 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC_COMPLETE]
2014-04-15 23:41:43.678664 [ALERT] switch_core_media.c:334 Looking for zrtp-hash
2014-04-15 23:41:43.678664 [ALERT] switch_core_media.c:289 Deciding whether to pass zrtp-hash between legs
2014-04-15 23:41:43.678664 [ALERT] switch_core_media.c:291 CF_ZRTP_PASSTHRU_REQ not set, so not propagating zrtp-hash
2014-04-15 23:41:43.678664 [ALERT] switch_core_session.c:2839 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC]
2014-04-15 23:41:43.678664 [ALERT] switch_core_session.c:2854 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC_COMPLETE]
2014-04-15 23:41:43.678664 [ALERT] switch_core_session.c:2839 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC]
2014-04-15 23:41:43.678664 [ALERT] switch_core_session.c:2854 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC_COMPLETE]
2014-04-15 23:41:43.678664 [ALERT] switch_core_session.c:2839 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC]
2014-04-15 23:41:43.678664 [ALERT] switch_ivr.c:1835 sofia/tone_detect/
xlite@129.sip.testy.com receive message [TRANSFER]
2014-04-15 23:41:43.678664 [ALERT] switch_core_session.c:2854 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC_COMPLETE]
2014-04-15 23:41:43.678664 [ALERT] switch_core_session.c:2839 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC]
2014-04-15 23:41:43.678664 [ALERT] switch_core_session.c:2854 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC_COMPLETE]
2014-04-15 23:41:43.678664 [ALERT] switch_core_session.c:2839 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC]
2014-04-15 23:41:43.698505 [ALERT] switch_core_session.c:2854 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC_COMPLETE]
2014-04-15 23:41:43.698505 [ALERT] switch_core_session.c:2839 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC]
2014-04-15 23:41:43.698505 [ALERT] switch_core_session.c:2854 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC_COMPLETE]
2014-04-15 23:41:43.698505 [ALERT] switch_core_session.c:2839 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC]
2014-04-15 23:41:43.698505 [ALERT] switch_core_session.c:2854 sofia/tone_detect/
xlite@129.sip.testy.com receive message [APPLICATION_EXEC_COMPLETE]
2014-04-15 23:41:43.698505 [ALERT] switch_core_session.c:2693 sofia/tone_detect/
xlite@129.sip.testy.com receive message [PROGRESS]
2014-04-15 23:41:43.698505 [ALERT] switch_core_media.c:334 Looking for zrtp-hash
2014-04-15 23:41:43.698505 [ALERT] switch_core_media.c:289 Deciding whether to pass zrtp-hash between legs
2014-04-15 23:41:43.698505 [ALERT] switch_core_media.c:294 No partner channel found, so not propagating zrtp-hash