Android VOIP App

Dear Sir or Madam, here are the main details of the project: I need an android app, that should be able to do prank calls with different szenarios like the german app „Marcophono“ or „Juasapp“, with the difference that my future app should use VoIP/IP telephony (with use of the provider sipgate). So here is how it should work: The user opens my app and can choose betwenn 1-5 free scenarios and 8-15 paid scenarios. After that, the user can typ in the number or load contacts from smartphone and choose one, then the app is going to call the pranked person. While calling, the user can press different buttons with audio messages(will be pre-recorded by me) I provide you. The pranked person should hear that [login to view URL] transfer between database and live call have to be instant. Each scenario could be between 10-50 audio messages and some variable like different fornames and surnames and some different car names and colours. The app will be in german language. I will provide all texts and audios to you. >>!!Please read also the attached document!!<< Best Regards Bashkim