Calling cards iPhone application

I am newbie to iPhone development, I want to do a kind of POC which fulfill the following requirement.

It will be basically a calling card application where user will enter a toll free number followed by pin number. After entering a pin no. it will show the available contacts from the iPhone itself, user will select a desired destination number and call it.

I know this is a whole new native application, but can anyone guide me how I can start wor开发者_如何学Pythonking on the same. I have collected a few information about what calling card is and how it works. I'm a bit confused about how can I get the information from calling cards service provider?. Do i need to call there API and how to do a code in the XCODE tool?

Please help me in this regard.

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A quick google of calling card api's shows that most card companies have them, but they also don't publish them. Looks like you'll have to talk directly with them and get api specs. It may cost you? I'm guessing the actual API won't be very complicated... a couple of HTTP requests and a little bit of response parsing. You might want to look into asi-http-request for building the requests, and you can probably do most of the response parsing with NSStrings or NSXMLParser if they use XML.