hi,
i spent one week to check this problem:
i have * with digium te110p card
zaptel
span=1,1,0,ccs,hdb3,crc4
bchan=1-15
dchan=16
bchan=17-31
loadzone = fr
defaultzone = fr
zapata
group=1
signalling=pri_cpe
context=from-zaptel
callerid=asreceived
channel => 1-15
channel => 17-31
hidecallerid=no
callwaiting=yes
usecallingpres=yes
callwaitingcallerid=yes
threewaycalling=yes
transfer=yes
cancallforward=yes
callreturn=yes
echocancel=yes
echocancelwhenbridged=no
echotraining=800
rxgain=0.0
txgain=0.0
pickupgroup=1
immediate=no
language=fr
context=from-zaptel
switchtype=euroisdn
signalling=pri_cpe
rxwink=300
green on card
i make a call every thing ok
4minutes after the call is hunged up
cli>
primary D-channel on span 1 up
primary D-channel on span 1 up
primary D-channel on span 1 up
primary D-channel on span 1 down
primary D-channel on span 1 up
primary D-channel on span 1 up
primary D-channel on span 1 up
primary D-channel on span 1 down
[color=red][b]
no possibility to make call untill i restart
etc etc etc
i do all changes, all rebuild, nothing 
plese please please HELP[/b][/color]