asterisk users - Dec 2006 - sip qualify unreachable/reachable - ci$co 7940

I have logs full with this messages...
I must have qualify turned on, because phone is behind firewall,
main problem si, that phone is each hour about one hour unavailable! :'(
I tried to modify minexpiry/maxexpiry sip.conf timeouts, but nothing 
help me.
I'm using latest firmware 8.4 in phone, will be better to downgrade? to 
what version?
(latest asterisk 1.4branch)


[Dec  7 00:36:56] NOTICE[19226] chan_sip.c: Peer '108' is now 
UNREACHABLE!  Last qualify: 205
[Dec  7 01:36:23] NOTICE[19226] chan_sip.c: Peer '108' is now Reachable.
(189ms / 2000ms)
[Dec  7 02:36:41] NOTICE[19226] chan_sip.c: Peer '108' is now 
UNREACHABLE!  Last qualify: 198
[Dec  7 03:36:22] NOTICE[19226] chan_sip.c: Peer '108' is now Reachable.
(199ms / 2000ms)
[Dec  7 04:36:38] NOTICE[19226] chan_sip.c: Peer '108' is now 
UNREACHABLE!  Last qualify: 177
[Dec  7 05:36:05] NOTICE[19226] chan_sip.c: Peer '108' is now Reachable.
(201ms / 2000ms)
[Dec  7 06:36:21] NOTICE[19226] chan_sip.c: Peer '108' is now 
UNREACHABLE!  Last qualify: 156
[Dec  7 07:36:02] NOTICE[19226] chan_sip.c: Peer '108' is now Reachable.
(177ms / 2000ms)
[Dec  7 08:36:19] NOTICE[19226] chan_sip.c: Peer '108' is now 
UNREACHABLE!  Last qualify: 210
[Dec  7 09:35:46] NOTICE[19226] chan_sip.c: Peer '108' is now Reachable.
(201ms / 2000ms)
[Dec  7 10:36:02] NOTICE[19226] chan_sip.c: Peer '108' is now 
UNREACHABLE!  Last qualify: 151