I've had this happen after flashing some ROMs (MIUI and older CM versions). It's a bitch to fix, and honestly its mostly trial and error. I did manage to get it to work, but I can't remember the exact series of things I did. You can tell its working correctly when it shows 4G/LTE (not just LTE) and you can still make phone calls, and you can send/receive texts and MMS.
Before trying any of this though, it might just be a KitKat issue -- you will lose a huge amount of reception running the stock 4.4.2 OS. When I tried it I was never able to get 4G due to the poor signals I was getting with KitKat. I would strongly recommend reflashing to the the last Jelly Bean stock firmware (skip gpt.bin and tz.bin) and see if you still have the no 4G issue. I'm running stock JB (with the garbage apps frozen) after trying every ROM out there, because the signals I get are way stronger, and the battery life (might be due to better signals?) is amazing -- I can go 2-3 days without a charge.
In any case, if you still want to try it, I think these settings are the ones you want (what worked for me was actually TOGGLING the settings to something else, then back to the correct ones). Also, this was under JB, but I think its identical with KitKat:
Go to Phone Info. Click the menu option and click on the Radio Bands. Change it to US Band. This will break everything.
Go back to the menu and Radio Bands. Change it back to Cellular.
Then scroll down and click on the Preferred Network Type. Change it to GSM/CDMA (Auto). At this point you should see the Location: showing actual info in the BID, SID, NID fields, and GSM will be "In Service", GSRM will be "Connected" and Network Type will probably be eHRPD (which is still 3G).
Click on the preferred network type again and change it to "LTE/CDMA/Evdo". It should change the GSRM to LTE. If not, power off, pull the SIM, power on. Wait for it to say SIM not found. Power back off, put in the SIM and power back on.
Go to your Settings, and under Wireless & networks click on More... and click Mobile Networks. Again, the fix was toggling, so if it says Global, change it to LTE/CDMA or if it says LTE/CDMA, change it to Global. It doesn't matter which one its set to (as long as its one of those 2 and you toggled it).
At this point, I had to let the phone sit for about 10-15 minutes. After I came back, it started switching automatically to 4G/LTE and you should be good to go.
If you can't MMS or text, go back to the Mobile Networks settings, click on Access Point Names, click the menu and reset to default. Power off and power back on.
Hope this helps... GL!
So, I got a new SIM, and things worked for a while, but when I tried to make a call, it said "Phone not authenticated". So I go back in, the guy says to dial *228, and 1 to activate. I do it, and the calling works, but I'm back to 3g. So I'm back in this boat again...while I get 4g in my Gnex, with the same Sim...
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