I am probably going to get the next iPhone too this summer. I am still on my 3G that I got a few weeks after it came out a couple summers back and had the original iPhone before that.
The HTC EVO, Sprint's first 4G phone is coming out soon and that looks really cool, though I don't live in a 4G area yet so not too interested. Also later in the year you start getting the Windows 7 phones which I think also have potential especially if you want to have real MS Office support on your phone.