Purchasing credits is easy and the more you purchase, the lower the cost per page. For example, sending a fax in the United States uses 10 credits per page. Purchasing the 600 credit package will cost you only 33 cents per page compared to 66 cents per page if you purchase the 15 credit package.
Number of credits / Cost for the US customers (may be different for the non-US customers, based on the Apple AppStore price tiers)
15 credits - $0.99
75 credits - $3.99
200 credits - $9.99
600 credits - $19.99