Payment option for shopping cart application iPhone SDK

I have been working on an shopping cart app for a retail store. They want us to enable payment option within the application. Using Paypal SDK its available in 4.1 and above but I heard it's not allowed by Apple. But I need to use it in iOS 3.0 onwards.

Is th开发者_C百科eir any other way to enable payments within application other than in-app purchase? I want to use it in iOS 3.0 onwards. Is their any solution to use it in iOS 3.0 and above.