I ride with a Terrano bluetooth/communication device mounted to the top of my bicycle helmet and, in order for it to work using all its features, I need my phone with me (to answer/make calls and to get detailed voice directions if needed). I also carry a custom made first aid kit in a small plastic snapped shut container that fits perfectly in my jersey rear pocket.

I place the operating side of my cell phone aimed towards my body inside my middle rear jersey pocket with the first aid kit in the same pocket on the outer side so that it protects the cell phone. Both cannot be seen as they fit in the pocket perfectly, in almost all my jerseys.