How to Redeem Skype Credit from a Voucher
Go to the following Web page: https://secure.skype.com/store/voucher/redeem.html
Click the Redeem button at the bottom of the page in the Redeem voucher section. Enter your voucher number in the Type in the unique number from your voucher or card box.
You don't have to specify the kind of Skype credit you are redeeming. From your voucher number, Skype can automatically tell what and how much you are redeeming.
Select the I Agree to the Skype Terms of Service check box and then click the Redeem voucher or prepaid card button.
Depending on what you are redeeming, you often get an instant confirmation.