I am in the EXACT place that you are. No joke. Ha. I too am with Sprint, and was trying to figure out what it was worth to me.
I will tell you that I hopped back and forth between getting a 7100 series or a 8700c, and went to cingular, they have a 7100g that is similar to the one nextel has, I tried to type out "Hi, My Name is Vikkie" on their phone pad, I didn't even to get to the "a" and gave up, I don't like how they have the qwerty keyboard broken up. Picked up the 8700c and tapped it out in less than a few seconds. Unless you don't mind getting over the learning curve, this was the biggest point that made me choose the 8700c
I am planning on keeping my sprint phone for my calls and text messaging, and using my Cingular 8700c just with the data plan to do the internet jazz and to use as my PDA, I figure if I decide I want to use it as a phone, I will just go add it on :D
I like how slim the 7100s' are but they come with a price. I cannot use their keyboard for nothing. The 8700c has won my heart