atm there is no way to auto-select for international calls. What you can do atm is utilize a different prefix, i.e. dial 9 for national calls, and 8 for international calls (just as an example).
OR if you want to dig in, get together with cfernandes and/or Alblasco1702 on IRC, so you guys can figure out changes to the dialplan to do outbound selection based on dial rules other than prefix as is right now.