There are a number of credit card processing applications in the iTunes Store, and at least a couple claim PCI compliance, if that's what you mean. Do a Power Search for apps with "credit card" and browse through the results, or search a site like appshopper.com. Once you find one, you can contact the developer and ask if they'll share tips.
If that's not what you're referring to, please post back and elaborate.
Regards.
Message was edited by: Dave Sawyer