I had one of these with a Treo several years ago and it wore like iron. After 2.5 years of use, not even 1 stitch had come undone. They have them for a wide variety of cases, bumpers, skins, and for the naked phone.
http://tuff-as-nuts.com/Belt-Cases-for-Apple.aspx
http://tuff-as-nuts.com/Belt-Cases-for-Apple.aspx