Asterisk Help FXO IAX

I am a newbie. I have an FXO card i wan that if a call lands on an FXO card it connects to a VSP in US over an iax channel. But once i call the number i ll get errors like
ZAP/1-1 trying to connect s not found some failur and warning message
pl help by give the complete config for extensions.conf and iax.conf
Nice regards