How can you set up multiple fax locations for POs?

We are updating to 9.1 and used customizations in prior releases to handle the fact that we have three local area codes that don't need a '1' in front of the fax number.  I would like to set this up in the 'fax location' page if possible (I think in the 'dialing area code' field .  Has anyone figured out how to have multiple local area codes for faxing of POs?

Thanks in advance.