Newbie Question 2: Selecting CO lines

I am thinking of using Asterisk to be our home PBX. We currently have the following setup:

3 incoming Vonage lines for my wife’s business
1 incoming Vonage line for our home
1 incoming Vonage line as a “guest” phone line
1 fax line

Here is what we would like to do:
When I pick up the phone and start dialing, that it would automatically default to our home line, HOWEVER if I dial “9”, then it would pick the first available business line.

Is this possible?