Not gonna happen unless you have two seperate inbound trunk groups or the carrier is sending you more than 4 digits.
If the carrier is only sending you 4 digits, example: 1234, the system doesn't know what extn to send the call to.
If your carrier is sending you 5 or more digits then you can tell the difference between what extension to send it to.
In that case, you will need to put the digits the carrier is sending in the system speed call form and point it to the actual number.
Ralph