Today I brought home my iPad Air and immediately began the process of setting it up and restoring it to the back up I had performed on my iPad mini in the morning. The restore completed and it began downloading all of the apps from the App Store. This is where things kind of take a turn for the worse.
I needed to leave for work, so I left which put all of my downloads on pause. When I arrived at work, I connected to my iPhone via tethering so that I could access the internet on my iPad. About 30 minutes later my iPhone had died. I couldn't figure out why it had died so quickly, but I plugged it in to charge anyway. I noticed while the phone was charging however that most of my apps had finished downloading. Evidently the iPad considers tethering to be a form of Wifi and decided to resume downloading my apps over cellular. So my phone was drained and shut off as a result.
When I turned my phone back on, it would never acquire a cellular signal. At first I thought it was just an issue with T-Mobile, but the signal did not return after 3 hours. I got home and checked my wife's cell service and discovered that her iPhone did not have any issues. Something was up with mine. So I tried to go in to the Cellular settings, but each time I attempted to the iOS Settings.app would crash. The device would randomly acquire an LTE signal for about 15 seconds, then the OS would hang momentarily and loose the connection. It would then resume "Searching" for an extended period of time (up to 15 minutes) before repeating the whole process again.
I reset the network settings and that did not seem to fix it, and that's when I decided to blow away my phone. I wanted to see if it was a software issue or if my phone had fried its cell chip due to pulling down all of those iPad apps over an extended period of time. I was greeted with a "Please disable Find My iPhone" message when I tried to erase my phone, due to having Find My iPhone enabled. That's when I realized it was not just cellular, but communication in general. Wifi was no longer working nor bluetooth. After calling and speaking with Apple briefly, I put the phone in to DFU mode and was able to circumvent the Find My iPhone requirement. I blew away the phone, restored from my last back up and everything seemed to work fine afterwards.
Moral of the story? Don't let your iPhone die out. Shut it off properly before the battery runs out!