These phones are pretty straightforward what I have found is that the antenna gets knocked loose very easily and maybe the new os is more finicky about signal strength. If you have dropped or bumped your phone it will pop off the antenna connector but stay connected enough for use but it will drop calls show no or very weak service signals. Easy to pop off back to check antennas just resent. There is a guide on fixing site. May not solve your problem but yah gotta start somewhere.
Look guys in my case it was the antennas once back was off the right side antenna looked connected but was not have to take plastic cover off clean and reconnect snugly it kind of snaps back on. Problems solved
Was having problem with dropped calls was antennas you need to undo them clean with IPA and snap securely should notice difference. Good luck Update (05/30/2017): You may also need to backup and reset phone.
unfortunately it is under the ear speaker housing and there are several gold contacts under the daughter card on the top of the phone.... Very hard to get to, must use heat to remove, and very easily damaged. I know I am currently looking for the part. Which doesn't exist anywhere. But found on some replacement lcds for sale.