Let the hive mind of Engadget get that for you.
"I just switched to Sprint from Verizon about three months ago for the Pre. Then I went for the Hero about a week ago. Now, I miss my hardware keyboard and am thinking about switching to the Moment. I am still able to switch back to Verizon if I want and get the Droid when it arrives. Should I just trade up to the Moment when it comes out, see if I like it, and if not switch to the Droid? Or something else entirely? Help!"
well Sprint does need it's "big phone" with all the other carriers now equipped with their exclusive, $200, touch screen touting, all around devices.
AT&T - iPhone 3G
T-Mobile - G1
Verizon - Blackberry Storm
Sprint - ? (i say your logic fits, especially with Palm's love of Sprint as it is)