Since sprint has their head in the sand and is ignoring the FLOOD of posts here of people having problems with this update - and asking for cross streets and other useless actions, here is how to get your phone back. Unfortunately, doing a factory reset won't fix it. Go to the Samsung Experience center at your local Best Buy store and tell them you want the previous version (L720TVPUBNAF), which was the KitKat update, flashed to your phone. You will lose everything on your phone but you will get a working phone back - with working data and Sprint Zone. And unlike going to a sprint store, you will not have to wait an hour to get your still unfixed phone back. Maybe Sprint will actually address this bad update eventually. But based on their clueless responses on this forum though, I won't be holding my breath on them fixing it. So we're on our own.
For those that are more hands on, you can download the firmware online and doing the firmware change via Odin. Go to xda developers and search for the phone to get more info.
The only problem with trying to load via Odin is there is no full NC6 ROM file available yet. There is also the possibility of tripping Knox warranty flag by downgrading the firmware. I didn't try it myself - it might work without tripping the Knox flag, but I just felt safer letting Samsung do it for me. And my Knox flag did NOT get tripped by what Samsung did. Again, it's possible Odin would load NAF just fine to a phone with NC6 already on it, I just didn't want to be a guinea pig with my new phone and take any chance on Samsung or Sprint saying I voided my warranty. Once a full NC6 ROM file becomes available, it might be safe to Odin that to your phone. I don't think the ROM itself is bad, it's just the update file that is doing something funky.