SIP Trunk setup on Asterisk

SIP Trunk can be set up in the "SIP Account" menu with following settings:

[Peer name]
type=peer
host=sip.mcntele.com
username=SIP ID
secret=SIP password
nat=yes or no
context=Context of call (dialplan context)
disallow=all
allow=alaw
dtmfmode=rfc2833
canreinvite=no
qualify=no
videosupport=no
t38pt_udptl=yes,redundancy,maxdatagram=400
insecure=invite
fromuser=SIP ID
fromdomain=sip.mcntele.com

Also you should have actual registration:

[general]

register =>; SIP ID:SIP password@sip.mcntele.com/extension number as destination for calls