This app is exactly what I was looking for, and I'm excited to practice with it, the only issue is that it's hard to control the volume of the calls b/c the volume buttons on the iPod/iPhone control the "Volume" while the app is open, but the sounds are governed by the level of the "Sound Effects", which cannot be changed in-app. This is a small fix that would make this app a lot less confusing at first, but otherwise, very well done!
Edit: With the latest update, the sound bar makes it easier to use, however it seems to still be quiet unless both Volume and Sound Effects are all the way up. Thanks nonetheless!!