Write an mobile application - repost 2

The following features are required: 1. A will install the music application, will start it. When A makes a call to B, the music application will start playing in background, and will be heard by A. 2. The voice and music will also be heard by B too. Same vice versa. This is the most important feature, rest can be discussed. Project will be based on native app development i assume, and i need it for iphone and android both