No, for the sites that offer to sell the gift cards for other countries they also tell you how to use them. (Any special conditions that have to be met, etc...) I'll look online later and post the link to one of them so everyone can see how its done.
Here's the how to from jbox.com. (I assume all the other stores work the same way)
Product type: iTunes Japan Music Card
Apple's iTunes Music Store is incredibly popular in Japan, with hundreds of thousands of tracks of great music from Japan available for 150 or 200 yen per song. For fans of Japanese music around the world it doesn't seem possible to buy through the Japan iTMS, without a Japanese address and credit card. There is a way, however -- using the Japanese iTunes Music Card from Apple! A prepaid card that's charged with money for music purchases, this is a great way for J-POP/J-ROCK fans all over the world to get access to Japan's top-name music directly through their Mac or PCs.
When you click the Add to Cart button for this product, you'll be able to choose a Music Card with the new denominations of 1500 or 3000 yen of credit on it. You can also choose to have the card sent to you normally through the mail from Japan, have the J-List staff send you a scan of your card number through email, or opt for both.
Once you have your iTMS Japan code, follow these easy steps:
Load iTunes on your Mac or PC. If you don't have it yet, download it from Apple.
If you've already got an account in your home country, sign out by clicking on the Account button in the upper left hand corner, then Sign Out.
At the bottom of the iTunes Music Store window, choose the Japan Store. The name may appear in kanji, but it's easy to find.
Click the Redeem button along the right side of the iTMS, and enter the scratch-off Redeem Code printed on the back of the card when asked.
iTunes will show you a dialog box asking for your current account. Since we're making a new iTMS account for the Japan store, click Create Account.
Follow the steps to create a new account, first agreeing to the iTunes agreement (step 1 of 3), then entering email, birthdate and vertification question (step 2).
Important: When signing up for an iTunes account with a pre-paid card, some customers have reported that iTMS won't let you proceed without entering a credit card. In order to bypass this, hit the "Home" button and begin the Redeem process again, and you'll see the "None" button the second time through. This is a known issue that affects Japanese users in Japan as well.
At step 3, where you are asked for your (Japanese) address. You can enter any address you like. Note that you must enter your name twice, once for "kanji" and once for "pronunciation" (but you can enter the same information into both fields). You can do this in English or any language that's supported by iTunes -- the ability to read Japanese is never required for the iTunes Japan Store -- so for the phonetic spelling you can just enter the same normal English characters as the other 'name' fields.
Enjoy purchasing great music and audio content directly from Japan in the Japan iTunes Music Store! Now that you have an account tied to a prepaid card, you can get full access to the "Free iTunes Single of the Week" from Japan, and future prepaid card credit can be added to your existing account.
Music from the Japanese iTunes Store is fully compatible with iTunes and iPods from any country. iTunes has no issues with maintaining multiple accounts in more than one music store. It couldn't be simpler! And best of all, you can surf and buy music from your iPhone (version 1.1.1 firmware or higher) or iPod Touch! Just make sure you're signed in to the Japan iTunes Music Store with iTunes when you sync the iPhone/iPod Touch and login data will be carried over.
