/etc/zaptel.conf

loadzone=de
defaultzone=de
loadzone = de
defaultzone = de
span = 1,1,0,ccs,hdb3,crc4
bchan = 1-15
dchan = 16
bchan = 17-31

/etc/asterisk/zapata.conf

[trunkgroups]
spanmap => 1,1,1
[channels]
switchtype=national
language=de
context=roitel
signalling=pri_cpe

usecallerid=yes
hidecallerid=no
callwaiting=yes
usecallingpres=yes
callwaitingcallerid=yes
threewaycalling=yes
transfer=yes
canpark=yes
cancallforward=yes
callreturn=yes
echocancel=yes
echocancelwhenbridged=yes
rxgain=0.0
txgain=0.0

immediate=no
group = 1
callgroup=1
dchannel => 16
channel => 1-15,17-31