Even if there is an app, it would never pass Apple's rules on apps. Since its a "sex" app it wouldn't get the green light.
iPhone SDK Agreement
3.3.12 Applications must not contain any obscene, pornographic, offensive or
defamatory content or materials of any kind (text, graphics, images, photographs, etc.), or other content or materials that in Apple’s reasonable judgment may be found objectionable by iPhone or iPod touch users.
Originally Posted by BigTee
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Yup, that is THE reason. Steve Jobs wouldn't know a good time if it reached up and bit him on his a**! Apple's so stodgy on this one, I receive magazines through Zinio, can't get Penthouse through the app, magazines with adult content are blocked.
There IS a way though. Create a website which conforms to the iOS mobile specs, won't be perfect, but would offer the mobile experience.