Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I was in the exact same situation...

I decided to buy the 16G 3G iPad (instead of the 64G) so I can buy the iPhone 4. After I got my iPad, I don't have the urge to upgrade to iP4 any more. My wife got it so I can play with it whenever I want most of the time but I don't feel the need for it any more. Don't get me wrong, it's something nice to have. I now have switched over to pre-paid and I carry my iPad all over the place now. Granted it's larger than iPhone and can't fit in a pocket but it fits alright in my little bag. And I just can't go back to surf the web or read/reply emails from the iphone any more. But that's just me.
 
I had the same dilema, but I got mugged the day after I got my 3G iPad. They took my wallet and first gen iPhone...:( When deciding which phone to buy as replacement it just felt unnecessary to buy a new iPhone so I went with a cheap nokia that can sync contacts with osx via Bluetooth. I am a student so I always carry a bag with books around so taking the iPad with me is not a big issue. so far i am fine with this setup.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.