According to a very scientific poll at everythingicafe, 41% of people put their iPhone in their right front pocket and 34% in their left front pocket. (http://www.everythingicafe.com/forum/threads/which-pocket-do-you-put-your-iphone-in.57830/).
I'm a right-front-pocket type but I hate it when my iPhone slips down to the bottom of my pocket and sits horizontally across my leg and it's worse (all bunched up) when I sit down.
I know, it's not the end of the world, but I decided to do something about it.
Step 1: Where the iPhone wants to go
Here's the shape of the front pocket and it is no surprise that the iPhone wants to slide down to the bottom.