asterisk users - Jun 2005 - Intelligent maximum channels solution?

Hi list!

I have an asterisk box connected to an ADSL connection that has 1 Mbit 
upstream. Is there any way to use max channels intelligently?

For example I would like to do some checks on the outgoing calls. When 
it's quiet I want each and every call to go out to my IAX provider.

However when more people start placing calls I would like to leave some 
room for the real expensive calls and switch chep (local) calls to the 
PSTN so expensive international calls can still be routed through the IAX 
provider.

I.e. allow 2 local calls and 1 call to a neighbouring country and still 
leave 3 channels free for calls to Japan or China that would be 
frightfully expensive from the PSTN.

This way I could squeeze the maximum benefit from the IAX / ADSL 
connection.

Thanks!