Edit sip.conf (/etc/asterisk/sip.conf) in your favourite editor and add the following example configuration:

[didforsale_1]
type=peer
host=209.216.2.211
nat=no
canreinvite=no
disallow=all
allow=ulaw
allow=g729
dtmfmode=rfc2833
insecure=very
context=from-trunk

[didforsale_2]
type=peer
host=209.216.15.70
nat=no
canreinvite=no
disallow=all
allow=ulaw
allow=g729
dtmfmode=rfc2833
insecure=very
context=from-trunk

After copying the above lines, save and reload Asterisk.