Sprint has very little 800MHz spectrum from Nextel/iDEN. They are going to run CDMA voice on it for sure. If deployed right, they could have just enough spectrum for one or two small LTE TDD channels.
Highly doubtful. That 800MHz spectrum is paired. For all intents and purposes, paired spectrum means FDD, not TDD. The most suitable spectrum for a TDD LTE deployment would be 2.5GHz spectrum that Clearwire has. Of course, they have so much of it that they also could divide it up and use it in an FDD configuration if they so chose. At this point, everything is just guesswork. It should be interesting to find out more on October 7th.
Some more info on LTE spectrum bands:
LTE Frequency Bands and Spectrum Allocations :: Radio-Electronics.Com