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!"
The difference between this phone and the EnV? Well, this is made to be cheap and a music player, for one. Its a totally different formfactor, its smaller and its lighter. Where the EnV launched for $250 or something, this is $100 now and will likely be cheaper before the holidays.
Enough differences?