Настройки в extensions.conf 
[bogon-calls]
include => lan-phones
exten => _9.,2,Congestion

[pstn-incoming]
include => lan-phones

[local-phones]
include => lan-phones
include => pstn-outbound

[pstn-outbound]
exten => _9.,1,Dial(SIP/${EXTEN}@192.168.11.120,20)
exten => _9.,2,Congestion

[lan-phones]
exten => 200,1,Dial(SIP/200,20)
exten => 200,2,Hangup
exten => 201,1,Dial(SIP/201,20)
exten => 201,2,Hangup
exten => 214059,1,Dial(SIP/214059,20)
exten => 214059,2,Hangup
exten => 214065,1,Dial(SIP/214065,20)
exten => 214065,2,Hangup

настройки из sip.conf

[192.168.11.120]
context=pstn-incoming
type=friend
host=192.168.11.120
insecure=very
dtmfmode=rfc2833
allow=all