As a confirmed Amazon user Kindle, fire TV and now fire stick, I can say personally it was the exclusive att thing that threw me off the fire phone, quite possibly the most stupid mistake they could have done.
Face it at this point there are two main phone camps, apple and android. It would have been nice to have greater access to all my amazon content, books movies etc but not enough to switch carriers. When my contract renews and if it's available on sprint I will likely buy it but face it no phone (anymore) is groundbreaking enough to switch providers for. The first apple phones were good enough but these days most of the differences are only of interest to tech writers, they are lost on the average user.