Rejoice. Apple has announced that promo codes will work for iPhone, iPad and iPod Touch users from around the world. Apple has mentioned it in iTunes Connect Dashboard that promo codes were made redeemable in all the app stores from December 8th 2010 onwards.
Since the launch of the App Store, promo codes were restricted only to the U.S. If a user living outside the U.S wants to redeem a promo code then he/she has to sign in with a U.S iTunes account, in order to get it done.
Now anyone from any country can redeem a promo code.
This has also been mentioned in the iTunes Connect Developers Guide