Free Ship to U.S. Only

How can I set up free shipping to the continental United States only with a coupon code? Will a module be required to accomplish this?
Using Version 2.0.3.1
Client ships Internationally
UPS & USPS shipping mods are installed and enabled

Thank you!

Super Coupons can create a coupon like this. You'd set it up like this:

------------------------------------------------------------------------------
COUPON #1
Title: Free Shipping Coupon
Code: (as desired)
Charge Type: Total
Charge Field: -100%
Rule: Geo Zone is USA
Rule: Total Value = Shipping Cost
------------------------------------------------------------------------------

Feel free to take a look at the screenshots and demo site, and if you're interested let me know at www.getclearthinking.com/contact if you have any further questions.

Thank you!