I got some hands-on time with iPhone 4 following today's WWDC Keynote address. My take? In short, it feels like a very nice, evolutionary upgrade to the 3GS. iPhone 4 isn't revolutionary - at least I don't think so today - but it feels like a solid, smooth smartphone with a killer feature in "FaceTime" video calling.

Video calling isn't new to smartphones - not even to American carrier smartphones, thanks to Evo 4G - but as Apple's FaceTime promo video showed, Apple is poised to market video calling on iPhone 4 like no other company to date has. Sprint should really pay attention because Apple's feature-driven marketing has paid huge dividends in the past, and TV ads showing Dads on video calls with their wives and new babies, and people signing to one another via video call really show features off in a way that tugs at heart - and purse - strings. Look for the new ads soon on a TV near you.

iPhone 4 also features an incredibly high-res screen that Apple's calling their "Retina Display," so named for its 326 pixels per inch resolution, which is actually sharper than the human eye can discern. The 3.5", 960 x 640 display is said to render everything from type to video smoother than any other screen on the market, and while I'm not so sure that the difference between "Retina Display" and "High-Res Super AMOLED Display" will be as huge as Apple would have us believe, iPhone 4's display looks great, without question.

iPhone 4 also features a 5MP camera with LED flash and new image capture technology that Apple claims does a better job of processing photos than other cell phones - resulting in sharper photos, particularly in low light. The video camera now captures 720p/30fps clips, and the flash works as a video light as well. Also, new is iMovie for iPhone, a full-on video editor that adds titles, photos, music, transitions, and Geotag-powered maps to the basic trim editing functionality of the iPhone 3GS' video editor. I didn't have the time to really dive into iMovie for iPhone, but at first glance it looks very, very slick - if perhaps a bit cluttered on the UI front.

As an object, iPhone 4 feels solid in hand. The edges are more squared off than those on 3GS, and I'll probably complain about that once the device ships later this month (I have very, very delicate mitts, you see). Just 9.3mm thick, iPhone 4 is thinner than the previous models, and Steve Jobs claims it's the thinnest smartphone in the world (somebody verify that in the comments, eh?). To me the phone felt noticeably more boxy than the outgoing model, but that's not necessarily a bad thing. A stainless steel band wraps around the perimeter of the device, and Apple says it's part of the phone's antenna system and results in improved reception. 

Video of iPhone 4 - and FaceTime - in action comin' right up!