Sorry for the late reply! I'm Michael, I helped make the Highline and have been using it daily with my iPhone 4S since I got it about 4 months ago.
Ginbill, I've drop tested it countless times, mostly to demo the that it's safe, and yes, my phone is fine. A friend I showed it to immediately used it to play Skip-It with her phone (um, not recommended). It's not going to come out from a simple drop.
Alli, current Apple charger cables have rounded hooks designed to easily remove from your iPhone. The hooks on the Highline are angled and so hold your phone snug. As cats have paws instead of opposable thumbs, they will not be able to remove Highline from your phone.
LVMHgirl, sorry to hear about your Blackberry experience. I was also concerned about the charging port when I first heard about the product concept. Fortunately, we were able to design something that won't damage your port under normal usage (stretching out the cord, dropping it). However, in our testing, using Highline to play tug of war is not a good idea (the port was still okay though!)
Again, sorry for the late post. Let me know if I can better answer any questions. Thanks!