Assemble a switch box to switch from listening to music on head phones to listening to answering your phone with your left ear, while music continues in the right.
(requires some electronic components, and basic soldiering skills)
Step 1: Explanation:
Hokai, so I was getting tired of having to take off my head phones when having to take a call, and I was wishing I could listen to music while on hold or on a boring call.
So the idea was born and after a quick trip to my local electronics store, so was the final product.