I suggest you go to a Sprint store and check out the form factor for yourself. They're getting seeded with them now, so call ahead first.

Myself, I put my 600 in my pocket, and I feel it's acceptable. The case it comes with adds a little bulk, so I take it out of that if I'll be walking far. The phone has a keyguard function, so it's not a big deal to keep it in your pocket, as long as you don't put your keys in with it! You can also pick up PDA screen protecters (clear plastic) that you can cut to fit the screen.

I haven't tried it with jeans yet, though. I mainly wear khakis and slacks.

There are also several belt clip type options already available, but I personally wouldn't be caught dead with one. Mainly because I fear the dude's from "Queer Eye" would be called for an intervention.