I have the same issue with SNOM 720 ver 8.7.2.9. If you dial into the conference e.g 71 what appears to be happening is that SNOM One does not play the welcome message. If you start to key in the password 000000 then after the 5th zero you get a message saying the password is incorrect. If you then type six zeros you enter the conference. If there is already an external call on the conference with a least one person, if you then call from the internal extension you can get a welcome message. (Having an external caller appears to improve the situation. ie. you get a welcome message but it is not guaranteed)
Here is a extract of the log when no welcome message is heard (and the conference has no exising participants):
[9] 2012/02/06 21:31:15: update_codecs for a246304fb301-krfb4lhsb5bw: adding codec pcmu/8000 to available list
[9] 2012/02/06 21:31:15: update_codecs for a246304fb301-krfb4lhsb5bw: adding codec pcma/8000 to available list
[9] 2012/02/06 21:31:15: update_codecs for a246304fb301-krfb4lhsb5bw: adding codec g722/8000 to available list
[9] 2012/02/06 21:31:15: update_codecs for a246304fb301-krfb4lhsb5bw: adding codec g726-32/8000 to available list
[9] 2012/02/06 21:31:15: update_codecs for a246304fb301-krfb4lhsb5bw: adding codec gsm/8000 to available list
[9] 2012/02/06 21:31:15: "update_codecs for a246304fb301-krfb4lhsb5bw: codec_preference size 6, available codecs size 6"
[6] 2012/02/06 21:31:15: Codec pcmu/8000 is chosen for call id a246304fb301-krfb4lhsb5bw
[9] 2012/02/06 21:31:15: Resolve 8590: aaaa udp 192.168.1.34 33891
[9] 2012/02/06 21:31:15: Resolve 8590: a udp 192.168.1.34 33891
[9] 2012/02/06 21:31:15: Resolve 8590: udp 192.168.1.34 33891
[6] 2012/02/06 21:31:15: Codec pcmu/8000 is chosen for call id a246304fb301-krfb4lhsb5bw
[7] 2012/02/06 21:31:15: Received RFC4733 DTMF on codec 101
[6] 2012/02/06 21:31:15: Received DTMF 1
[8] 2012/02/06 21:31:15: call port 125: state code from 200 to 200
** At this point I hung up the line
[9] 2012/02/06 21:31:34: Resolve 8591: aaaa udp 192.168.1.34 33891
[9] 2012/02/06 21:31:34: Resolve 8591: a udp 192.168.1.34 33891
[9] 2012/02/06 21:31:34: Resolve 8591: udp 192.168.1.34 33891
[8] 2012/02/06 21:31:34: "Remove leg 632: call port 125, SIP call id a246304fb301-krfb4lhsb5bw"
[8] 2012/02/06 21:31:34: "Clearing call port 125, SIP call id a246304fb301-krfb4lhsb5bw"
[8] 2012/02/06 21:31:34: Hangup: Call 125 not found
And an extract of the log when there is already at least one external another caller is already in conference:
[9] 2012/02/06 21:33:03: update_codecs for 0d47304f1240-b4xbuxmb992l: adding codec pcmu/8000 to available list
[9] 2012/02/06 21:33:03: update_codecs for 0d47304f1240-b4xbuxmb992l: adding codec pcma/8000 to available list
[9] 2012/02/06 21:33:03: update_codecs for 0d47304f1240-b4xbuxmb992l: adding codec g722/8000 to available list
[9] 2012/02/06 21:33:03: update_codecs for 0d47304f1240-b4xbuxmb992l: adding codec g726-32/8000 to available list
[9] 2012/02/06 21:33:03: update_codecs for 0d47304f1240-b4xbuxmb992l: adding codec gsm/8000 to available list
[9] 2012/02/06 21:33:03: "update_codecs for 0d47304f1240-b4xbuxmb992l: codec_preference size 6, available codecs size 6"
[6] 2012/02/06 21:33:03: Codec pcmu/8000 is chosen for call id 0d47304f1240-b4xbuxmb992l
[9] 2012/02/06 21:33:03: Resolve 8602: aaaa udp 192.168.1.34 33891
[9] 2012/02/06 21:33:03: Resolve 8602: a udp 192.168.1.34 33891
[9] 2012/02/06 21:33:03: Resolve 8602: udp 192.168.1.34 33891
[6] 2012/02/06 21:33:03: Codec pcmu/8000 is chosen for call id 0d47304f1240-b4xbuxmb992l
[8] 2012/02/06 21:33:04: call port 126: state code from 200 to 200
[8] 2012/02/06 21:33:04: Play audio_en/co_welcome_conference.wav
[8] 2012/02/06 21:33:04: call port 127: state code from 200 to 200
[8] 2012/02/06 21:33:06: Play audio_en/co_enter_pin.wav
[8] 2012/02/06 21:33:06: call port 127: state code from 200 to 200
[7] 2012/02/06 21:33:10: Received RFC4733 DTMF on codec 101
[6] 2012/02/06 21:33:10: Received DTMF 0
[8] 2012/02/06 21:33:10: call port 127: state code from 200 to 200
[6] 2012/02/06 21:33:10: Received DTMF 0
[6] 2012/02/06 21:33:11: Last message repeated 5 times
[8] 2012/02/06 21:33:11: Play audio_en/co_right_pin.wav
[8] 2012/02/06 21:33:11: call port 127: state code from 200 to 200
[8] 2012/02/06 21:33:12: Play audio_en/co_there_is.wav[9] 2012/02/06 21:33:03: update_codecs for 0d47304f1240-b4xbuxmb992l: adding codec pcmu/8000 to available list
[9] 2012/02/06 21:33:03: update_codecs for 0d47304f1240-b4xbuxmb992l: adding codec pcma/8000 to available list
[9] 2012/02/06 21:33:03: update_codecs for 0d47304f1240-b4xbuxmb992l: adding codec g722/8000 to available list
[9] 2012/02/06 21:33:03: update_codecs for 0d47304f1240-b4xbuxmb992l: adding codec g726-32/8000 to available list
[9] 2012/02/06 21:33:03: update_codecs for 0d47304f1240-b4xbuxmb992l: adding codec gsm/8000 to available list
[9] 2012/02/06 21:33:03: "update_codecs for 0d47304f1240-b4xbuxmb992l: codec_preference size 6, available codecs size 6"
[6] 2012/02/06 21:33:03: Codec pcmu/8000 is chosen for call id 0d47304f1240-b4xbuxmb992l
[9] 2012/02/06 21:33:03: Resolve 8602: aaaa udp 192.168.1.34 33891
[9] 2012/02/06 21:33:03: Resolve 8602: a udp 192.168.1.34 33891
[9] 2012/02/06 21:33:03: Resolve 8602: udp 192.168.1.34 33891
[6] 2012/02/06 21:33:03: Codec pcmu/8000 is chosen for call id 0d47304f1240-b4xbuxmb992l
[8] 2012/02/06 21:33:04: call port 126: state code from 200 to 200
[8] 2012/02/06 21:33:04: Play audio_en/co_welcome_conference.wav
[8] 2012/02/06 21:33:04: call port 127: state code from 200 to 200
[8] 2012/02/06 21:33:06: Play audio_en/co_enter_pin.wav
[8] 2012/02/06 21:33:06: call port 127: state code from 200 to 200
[7] 2012/02/06 21:33:10: Received RFC4733 DTMF on codec 101
[6] 2012/02/06 21:33:10: Received DTMF 0
[8] 2012/02/06 21:33:10: call port 127: state code from 200 to 200
[6] 2012/02/06 21:33:10: Received DTMF 0
[6] 2012/02/06 21:33:11: Last message repeated 5 times
[8] 2012/02/06 21:33:11: Play audio_en/co_right_pin.wav
[8] 2012/02/06 21:33:11: call port 127: state code from 200 to 200
[8] 2012/02/06 21:33:12: Play audio_en/co_there_is.wav