Here’s a problem I don’t have an answer to. If you use the built-in balance control on iOS to move the balance to left or right, this setting is over-ridden during a mobile phone call. Worse still, even high-end headphones like Sony or Bose rely on the built-in iOS balance. (They do not have their own balance adjustment.) I have not been able to find an app that can override the iPhone settings. If you just want to listen to a phone call in one year the only workaround is to use earbuds and take one out. I’m serious!
If you’ve found an app that controls the audio balance during a phone call let me know in a comment below.