It’s easy to buy Skype Credit in Skype Manager. You can pay for Skype Credit using a credit card, PayPal, and lots of other ways. If your has a registered United States address and has been verified, you can pay for Skype Credit in Skype Manager using an American Express (AMEX) card.
When you sign up for Skype Manager, you are given a limit that determines the maximum amount of Skype Credit you can purchase in one go. The range of payment methods available to you is also limited, so you may not be able to purchase Skype Credit with a credit card.
If your company is verified, you can access a wider range of payment methods or increase your purchase limit.
For more information on Skype Manager, there is a Quick Start Guide, a User Guide and several tutorial movies available on the Guides page of the Skype Support site.