I have an iPhone and iPad and use both. The iPhone is for whe I don't have the iPad with Me and most for phone and location apps. iPad is for web and media, but I can fall back to iPhone if needed.
I have both and I love both. You can't carry the iPad with you everywhere. Not to mention the fact that the iPhone is, well, a phone. I think of my iPhone as a miniature iPad now. And for me, the iPhone is indispensable because I tether it to my iPad for Internet access everywhere. I live in Korea now, and the 3G speed is out of this world. I could have bought a 3G iPad, but I saved some money and got the WiFi only model because of the tethering.
My iPad experience has caused me to long for (pine for, actually) an iPhone or at least one of the better android phones. We signed a new contract with Verizon for BB Storm 2's in February. Considered the iPhone but couldn't go with ATT's sketchy service in our area. Now that I have the iPad, I have a better idea of what I'm missing with the BB in terms of mobile browsing and apps. Please, Apple, bring the iPhone to Verizon!
Likely won't happen with the iPhone for a while, or at least the 5 year exclusive AT&T\Apple contract is up. But you should check out the current Verizon Android Phones. I have a Droid, and it's great. I just 'rooted' my droid to get Android 2.2 on it as well as WiFi tethering. This way if I ever take my iPad out of the house, I can just connect threw my Droid via Verizon 3G.
I have both ipad and iphone. I traveled alot on business meeting customer and doing alot of one to one presentation. iPad with Keynote is just the perfect tools for presentation. My other use is watching movies.. laptop is just not as mobile as the iPAD..
iPad is more of a Netbook replacement, as I see it. I had a netbook that I just recently sold to replace it with the iPad. For what I bought it for, I think the iPad will see more use.
I think the real question is "What is the point of having an iPhone if you have an iPad?" I ditched the smartphone and just carry around a basic small phone now.