Android or iPhone 2D barcode reader application

This simple project is about creating an Android or iPhone (3GS) application that will mainly use the camera to decode 2D barcode. The application storyboard will be: 1 - At app launch GPS coordinates will be retrieved (in background) and the user will have to fill a text field for reference, 2 - he will then read several barcodes. Once this step is validated the gathered data will be formatted as simple XML and then posted to a REST-like server, 3 - Exactly same thing but with a different attribute (but should be the exact same code). This storyboard should be implemented as sequential screens so that the user can go back and forth from step 2 to step 3 with ease. Each time he completes a step the related new data is posted. Usage of ZXing library or such copyrighted library is permitted. Special attention to performance on reading the barcodes is REQUIRED.