I hadn't thought about it until I got my phone home, but the sensor works just fine with the 3GS. As expected, the app is identical to that on the touch, although Apple posted a tech note regarding answering calls while using the Nike app, something you don't worry about on the touch. If you've never tried using the Nike sensor with either a touch or the iPhone, read on. Oh, and I don't have a Nike remote watch doohickey, but apparently those will work on the 3GS as well. If the Nike thing isn't your bag, we ran down some competitors a while ago.
To pair the device, go to Settings > (in App-specific settings) Nike+iPod and flip the switch to ON. At the bottom (you can see in our gallery) choose either Sensor or Remote, depending on what you've got, and you'll be prompted to move around (sensor) or press a button (remote). That's all there is to it -- the proprietary wireless connection kicks in and pairs the two devices instamagically.
Just like previous iterations of the Nike system, you can change the PowerSong, voice, and units. One new twist: a new Lock Screen pref that will alter the locked-screen display to read in portrait or 2 available landscape modes. Very handy if you have a mount on your treadmill. What, you don't have a mount on your treadmill? Me either.
Now, after pairing, you should have a shiny new app on your screen that has the Nike logo and a plus sign. Unfortunately, my sleepy morning eyes couldn't find the app, but a Spotlight search found it for me. Here's Apple's notes on setting things up.
Keep reading for a short round-up of how the unit works while running.
Once I found the app, it was a trivial matter to get started. You select what type of workout you want (I generally choose a simple time limit) and start moving the sensor. Of course, you can just choose "basic" and start running, and it'll keep track. Or choose distance or a caloric goal. There's also a calibration tool, which seems easier to use because of the big, shiny buttons. Plus, you can calibrate for walking stride and running stride.
You can save workouts with specific goals in the "My Workouts" view in the app. A History view provides a quick summary of your runs, but with only one in the queue so far, I'm not sure how well it tracks over the long haul. Naturally, Nike would rather you go to their site and indulge their Flash-based app-mania to see graphs and other goodies. (I would happily pay money for an app that showed me a simple graph, just so you know, Apple and/or Nike.)
Anyway, in practice the app is simple enough. You can play/pause using very large buttons, see your progress along whatever goal you set on the big green bar up top, skip songs, play your "power song" and end the workout all from one convenient interface. You can also do most of these things from the lock screen, which is presumably what you'll see once your iPhone darkens the screen. While you run, as expected, you'll get timed reminders by voice of how far you've gone. When you wake the device (meaning, hit a button to awaken the screen), it'll also announce your current progress.
So what happens if you want to do other things while running or walking? First, as I advised earlier, be careful. It might be fun to tweet while jogging through the park, but running headlong into a lamppost hurts no matter what. The Nike app appears as a backgrounded app, with a large red bar across the top of the iPhone's Springboard (the pages of apps) and other apps. I didn't try this with apps like Space Defense, Sway, or other fullscreen games, but I wouldn't recommend it to begin with. Instead, as you can see in the gallery, I did tweet while running. It worked great and it was one click to get back to my workout screen.
Unfortunately this app only works with the 2nd-generation iPod touch and the newest iPhone, our now less-spacey 3GS. Sorry 3G folks, another onion in the ointment for you, I guess. Don't worry, in a year we smug 3GS owners will get our comeuppance when Apple introduces the 4G X Y (three blank spaces after the name).
If you already have a Nike+iPod sensor and just got a 3GS, however, this is terrific. I had been slogging along with my nano mostly for workout purposes, but it looks like I can finally hand that down to someone else. Now I just have to remember to properly safeguard my iPhone from sweat damage. Oh, and if you're cheap like me, you can fashion your own sensor strap using some rubber bands and duct tape, as I did over on DIY Life long ago -- or check out these other hacks and mods here. Enjoy!