Speaking of the LTEvo release, that's very interesting!
For those who missed it, courtesy of Sgt. Slaughter, one guy has May availability in writing from Sprint.
xda-developers - View Single Post - HTC EVO 4G LTE News-Videos/Pics [Official Thread]
So. It's May.
PS - ok to puzzle out availability of the Samsung, but I think that I'll move those to the SGS3 thread.