the NUT : normal phone use
Even though your iPhone is encased in a complete hard shell, you can still use your phone as normal, with only a very marginal reduction in speaker volume.
In fact, it is this hard shell which helps. The rigid plastic transfers the sound to the outside of the NUT, allowing you to listen to music, take calls, watch movies, play games and do pretty much everything your phone is capable of. With specially designed mic and speaker pickup channels, you can hear and be heard.
And if - for whatever reason - you wish to maximise 100% of the available speaker volume, simply unclip the lid. The iPhone is held firmly in place and the microphone and speakers are completely uncompromised.