I am not all that happy yet. I live on a fringe of an official 4G roll out, Houston. But while the service is going in, I am experiencing times where the other person cannot hear me. I use a hack where I force roam on Verizon using Verizon PRL's, and other Sprint PRL's, this seems to help some. But there are issues for sure. A Sprint retention specialist explained that even as the 4G rolls out, there is tweaking to do, etc. to get things all OK, even if the signal for 4G is strong, you might experience issues in some areas.
I wish we could just switch to CDMA only, there is a toggle for that, and just use 3G, until 4G is better, but that is not working any better for me. This issue does not happen to the degree it does on my GN2 4G phone, on our other 3G phones (iPhone and Pre).