Saw this on my Nexus 5 in the debug section. Was wonder what Band 51 was? I know that Sprint only uses Bands 25, 26, 41 in the US and was wondering why is Band 51 being selected. I noticed that is switches to this band whenever my phone gets down graded to 3G with the whole eCSFB situation in my area. (LTE works fine on my wifes iPhone 5c, but my Nexus 5 always gets down graded to 3G in my area.) Just wanted to know if anyone else knows why this Band shows up and what it means.
So they just place it in a default unsupported LTE band so that it defaults to 3G? I've been able to manually turn on the LTE antenna going to *#*#4636#*#*. But because I'm forcing the phone to only accept LTE signals it won't auto switch to CDMA to make phone calls. It connects in the area on Band 25 so I know it has the capability to connect here on LTE. Just with the tower upgrades they can't auto switch it on the TriBand phones yet. Kind of sucks.
It's not being placed in an unsupported LTE band so it defaults to 3G...that's just what the phone shows when it isn't connected to LTE. Instead of not showing anything...it shows 51. Until they fix the towers in your area, not much you can do.