From Wengowiki

Sip.conf

• register => sipusername_wengo:mdpsip_wengo@voip.wengo.fr:/sipusername_wengo
• [wengo]
  • type=peer
  • qualify=5000
  • fromdomain=voip.wengo.fr
  • fromuser="sipusername_wengo"
  • username="sipusername_wengo"
  • secret="mdp_sip_wengo"
  • host=voip.wengo.fr
  • realm=voip.wengo.fr
  • outboundproxy=213.91.9.206
  • outboundproxyport=5060
  • disallow=all
  • allow=gsm
  • allow=ulaw
  • allow=alaw
  • dtmfmode=RFC2833
  • insecure=very
  • callerid="Wengo nickname"
  • context=from_wengo
  • nat=yes
  • carinvite=no

Extensions.conf :

Please not that the following is only an example :

• [default]
  • include => from_wengo
  • include => to_wengo
• [from_wengo]
  • exten => sipusername_wengo, 1, Dial ...
  • exten => sipusername_wengo, 2, Hangup

You can create a context to make calls from a SIP user connected to the asterisk. For example :

• [to_wengo]
  • exten => _0., 1, SetCallerID("Lastname First Name")
  • exten => _0., 2, Dial, SIP/${EXTEN}@wengo
  • exten => _0., 3, Congestion or other...

Then make your own dialplan.