I can highly recommend modifying an Encased belt clip for shoulder strap use. I have been doing this for years and my phone has never fallen out even after hundreds of miles of brush bashing. All the folks I hike/hunt/ski with have either made their own or I did the conversion for them.
Buy the case/belt clip combo. Break the belt clip piece off the carrier. Cut 4 slots in the case with a dremel tool. Sew a short length of 1″ grossgrain (for reduced bulk) through a Slik Clip and then sew a tail of Velco omnitape to that (and make 2 of these). Thread these through the slots and then attach the Velcro tails to each other to snug the Slik Clips against the back of the case carrier. Voila. Easy one-handed operation.


