Asterisk

 iax configuration  ( not guaranteed ) 
 Working iax configuration, using vpn  Registration statement on one instance only ( Really vpn should not need a register statement ) 
 working iax config using nat firewall  Very similar to above but using nat instead of vpn.
 Configuring chan_mobile 
http://www.mhspot.com/sts/siptosis_skype_trunk_howto.html