AVService -- I want you to have faith in what I am about to recomnmend to you. I think most people in the U.S. don't think it's possible to carry an iPhone dangling on a lanyard around your neck, but the young folks in Asia do it ALL THE TIME.
I got my iPhone this past June, and I wear my iPhone this way EVERY SINGLE DAY. Trust me on this.
Go get yourself a Danglet. You can buy it from Amazon (
Amazon.com: Danglet Wrist and Neck Strap Adapter for iPod iPhone Touch: MP3 Players & Accessories)
Basically, it's a little plastic piece that snaps into the iPhone's charging port. It's got a couple of tiny prongs on the side that snap into place, and your iPhone will NOT fall off!!!
Just make sure never to yank the lanyard (always remove the Danglet by first squeezing the buttons together to pull the prongs in), and never twist that plastic piece (I don't know what will happen but I can see parts snapping off).
Like I said, I wear this EVERY SINGLE DAY. I've pasted a transparent business card holder on a clear plastic iPhone case, and I wear my work ID right on my phone, which I wear EVERY DAY.
If you absolutely cannot trust the Dangle to do its job, there are instructions out there for gluing laces onto iPhone cases so you can wear it around your neck that way. Up to you.
When I'm at work, I often wear clothes with no pockets or belts. And I don't want to carry my purse around with me everywhere. Using the Danglet ensures I have the phone with me at all times, and I love it!
PS: Since you're worried about tough environments; put whatever case on it that's relatively thin but that still leaves the port open. When you need to be outside where you're worried about your iPhone, you can buck it into your shirt like I do. Since it's dangling from your neck, you don't have to worry about not having a pocket!