After browsing for a while and looking for an iPhone sketch paper I could print out to jot down some ideas for an app, and not (yet) wanting to spend a lot of $ for a really cool notebook, I discovered: the only good option was offline. So I took a photoshop sketch someone had made (which actually _was_ online) and traced it in Illustrator. Maybe someone will get a kick out of it and I’ll spare them a couple minutes making one of their own. Here is mine, as PDF (A4 paper, not chip!) and EPS, if you want to get funky with it.
Update: I added little rulers that indicate 20px increments.
Update: I made a post with iPad-sized sketches. Check it out.