My S4 upgraded to Lollipop a few weeks ago. Since that time, the cell service stinks! The signal strength dropped and if the phone doesn't see a strong enough signal reasonably soon, the cell radio turns off and won't turn back on regardless of signal strength. The phone must be restarted to turn the radio back on. As an on call telecommuter, not having a reliable cell phone is a major issue. I've replaced the SIM card and done the factory reset both to no avail and with much pain! Any suggestions?