asterisk users - Sep 2005 - dialplan to try VOIP providers if they can't terminate call

I am trying to figure out how to try different VOIP providers if they
aren't able to terminate the call because they don't offer service to
that dialing area.

The error that gets logged to the console is:

Sep 13 00:01:43 WARNING[22093]: chan_iax2.c:6835 socket_read: Call
rejected by x.x.x.x: No such context/extension

The dialstatus returned is "No Answer"

I could check for that dialstatus, but it is the same dial status as
if someone didn't pick up the phone.

How are