zapata.conf

[channels]
language=en
group=1
pickupgroup=1
context=from-pstn
signalling=fxo_ks
usecallerid=yes
hidecallerid=no
callwaiting=yes
callwaitingcallerid=yes
threewaycalling=yes
transfer=yes
cancallforward=yes
callreturn=yes
echocancel=yes
echocancelwhenbridged=yes
rxgain=0.0
txgain=0.0
immediate=yes
musiconhold=default
channel => 1

zaptel.conf

loadzone        = us
defaultzone     = us
fxsks=1