Why the trunk hang ?is this phone or elastix issue

hiii ,

my specificatios is :

ame Package Name Version Release
Kernel
Linux(i386) 2.6.18 238.12.1.el5
Name Package Name Version Release
Elastix
elastix 2.2.0 14
elastix-firstboot 2.2.0 5
elastix-system 2.2.0 14
elastix-email_admin 2.2.0 9
elastix-vtigercrm 5.1.0 8
elastix-extras 2.0.4 4
elastix-asterisk-sounds 1.2.3 1
elastix-my_extension 2.2.0 5
elastix-agenda 2.2.0 5
elastix-a2billing 1.8.1 16
elastix-addons 2.2.0 4
elastix-im 2.0.4 2
elastix-pbx 2.2.0 14
elastix-security 2.2.0 7
elastix-reports 2.2.0 6
elastix-fax 2.2.0 4
Name Package Name Version Release
RounCubeMail
RoundCubeMail 0.3.1 10
Name Package Name Version Release
Mail
postfix 2.3.3 2.3.el5_6
cyrus-imapd 2.3.7 12.el5_7.1
Name Package Name Version Release
IM
openfire 3.5.1 2
Name Package Name Version Release
FreePBX
freePBX 2.8.1 7
Name Package Name Version Release
Asterisk
asterisk 1.8.7.0 0
asterisk-perl 0.10 2
asterisk-addons 1.8.7.0 0
Name Package Name Version Release
FAX
hylafax 4.3.10 2rhel5
iaxmodem 1.2.0 1.1
Name Package Name Version Release
DRIVERS
dahdi 2.4.1.2 5
rhino 0.99.4 2.rc1
wanpipe-util 3.5.2

i always find that a spesific account is hanged for tens of hours and busy my trunk line
as you see from the image below that the trunk line is busy for 16 hours !!!

my question is , is this an elastix issue or may be phone issue ??