Cellular data not working since 5.1 Lollipop flash Cellular data stopped working immediately after "upgrading" to 5.1-lollipop OTA (from 5.0.2) on my Nexus-4.  I am seeing the exclamation point in the signal strength indicator at all times, except when Wifi is on and connected. Voice calls work fine. Wifi works fine. 2 hours on the phone with Simple Mobile, then 2 hours back and forth with Google support, and still no resolution. So far I have tried:


Erase and reprogram APN settings
Remove and reinstall existing SIM card (that was Simple Mobile's suggestion, although I think if voice is working SIM is probably OK. I don't have a spare to try right now.)
Turning phone off and on
Reboot in Safe Mode
Turning Cellular Data switch off and on
Turning Airplane mode off and on


The exclamation point on the cellular strength icon seems to follow the exclamation point on the Wifi icon, i.e., both go on and off at the same time--when a Wifi connection is made or broken.  Is it possible that this may be a bug related to an accidentally shared variable between the two?

Google 2nd level support has said they don't have an answer.  They want me to try a new SIM card, which I'm trying to get from Simple Mobile.  If that doesn't work they want to "discuss repair options for the phone."

I've seen some other people with similar problems but haven't seen any fixes or workarounds other than what I've already tried.  Does anyone have any ideas?
I'm back up and running.  Here's what I know at this point.  I'm posting it here because I think many people may experience the same behavior.

After much back and forth with Simple Mobile (note that they share some infrastructure with T-Mobile, Tracfone, etc., so users of those services may be affected as well) they found that my cellular data had been disabled on their end.  Nothing was wrong with my account, indeed, voice continued to work normally, it was just the data that had been disconnected.

I asked why this happened and the 2nd-level support person told me that they are still investigating but one thing that's possible is that a change in 5.1 Lollipop caused something to fail on their end.  She said they have been receiving numerous trouble calls with the same symptoms, all with phones recently upgraded to 5.1.  

So, allowing for the typical misinformation that we all get from customer support, this actually seems like it's plausible.  I don't want to spread misinformation, but if anyone else is tearing out their hair with these symptoms, try leaning hard on your carrier to check your line.