If you want to limit domestic shipping to the Continental United States, you can alter the code in shopping/checkout/shipping/act_calc_shipping.cfm line 30.

This:

    if (CompareNoCase(check_country, Request.AppSettings.HomeCountry) IS 0)
        ShipLocation = "Domestic";
    else
        ShipLocation = "International";

gets changed to this:
   
    if (CompareNoCase(check_country, Request.AppSettings.HomeCountry) IS 0 AND
        NOT listfind("HI,AK,AA,AE,AP,AS,GU,PW,PR,VI", GetShipTo.state))
        ShipLocation = "Domestic";
    else
        ShipLocation = "International";

This excludes Hawaii, Alaska, Military Posts (AA, AE, AP, AS), Guam, Peurto Rico, Virgin Islands.