Detecting invalid Area codes


#1

Does anybody know how to detect an invalid area code with Asterisk? We have a number for example that is a valid number but the area code does not exist. When I dial it with my SIP phone I get a funny scracthy silence and then it hangsup after about 10 seconds or so. If I call that same number via my cellphone I get the fast busy signal.

Is there a way that Asterisk can detect that and send me back a fast busy signal?

Thank you.
Gerhard