EDIT:

This last week at work I started noticing that my data and voice would drop off and I would get the icon showing half signal but would have an ! In the icon. When I look at the Sim status it shows I'm connected but I'm not. After rebooting the phone I will have 4G service for about 20 minutes then it drops off again.I have Tmo and contacted support and they told me to reset the APN but that didn't help.The only thing that looks new on my phone is a recent app called Google Connectivity Service.Other people at work on Tmo are not experiencing this issue but they are on Kit Kat still. I don't have this issue at home, I get full LTE there.This is still broken as of 05/20/2015 -- Possible workarounds can be found here (thanks TaintedByte).