This is thus going to be a very brief post with just the settings for freecall.com, which offers a SIP service.
The specific settings that you need to make are (this is from my ~/.linphonerc
[auth_info_0] username=myUserId userid=myUserId passwd=PasswordInPlainText realm="sip.freecall.com" [proxy_0] reg_proxy=sip:sip.freecall.com reg_identity=sip:myUserID@sip.freecall.com reg_expires=3600 reg_sendregister=1 publish=0 dial_escape_plus=0
Yes, that's it. So, there you go - you now have a reasonably priced alternative to Skype for international calling.
I've charged my account with 10 Euro, and I've made a few test phone calls. So far so good.
See http://verahill.blogspot.com.au/2014/06/581-obi200-and-debian-and-iinet.html for how to use the obihai 200 ATA with freecall.