No way in hell would I trade in my iPad. I love this thing from the time it was only a rumor. Now when it's in the basement or whatever I look at my phone and if I'm not willing to go get my iPad I wont bother browsing the web.
I definitely wouldn't, i have a 3GS and not enough money for 4 otherwise I'd have it... But I have grown to love the iPad and some feature might be similar but to me it's more pleasant using the iPad for web and well pretty much everything else, my iPhone now only gets used for camera, text and phone calls unless I am out and badly need to check something where wifi isn't available. (also due to my iPad seeing a lot more usage then my iPhone my iPhone battery is now awesome and lasts days without charge, before iPad I barely got a day heh)
Definitely not. I got my iPad after my iPhone 4 and I would not part with it for nothing. If I didn't have the iPhone I'd have a blackberry or an android but like someone stated earlier, you can get an iPhone for $200 and my iPad cost me $729 so it's definitely not an even trade at all.