[channels]
language=en
context=BTInbound
signalling=fxs_ks
usecallerid=yes
hidecallerid=no
callerid=asreceived
echotraining=yes
echocancel=yes
echocancelwhenbridged=yes
rxgain=9.0
txgain=5.0
switchtype=national
channel => 1

extensions.conf

[BTInbound]
exten => s,1,Zapateller()
exten => s,2,Dial(SIP/2001&SIP/2002&SIP/2003,60,Ttr)