Many call center owners and IT's were asking us for the configuration of their Switch2Voip VoIP account on Vicidial, here is what works for us and many others.
[Switch2Voip]
username={USERNAME}
type=peer
secret={PASSWORD}
progressinband=never
port=5060
nat=auto
insecure=very
ignoresdpversion=yes
host=sip.switch2voip.us
dtmfmode=rfc2833
context=from-trunk
canreinvite=no
allow=g729&g711&g723
fromuser=+{CALLER ID}
Registration
register=>USERNAME:PASSWORD@sip.switch2voip.us/siptrunking