I'm facing the same problem with my iphone 5S, I even tried the restore option from itunes and the problem became worse, now I can't activate my iphone nor restore the backup.
I have noticed that after the update through the iphone update option my modem firmware value became blank. Of course now I can't access anything as I restored through the itunes and it requires service to activate the iphone.
p.s. Before updating through itunes I tried to resolve the problem through resetting network, restarting iphone, putting the iphone on airplane mode but nothing worked.
Apple please help !!!! Make a new update that fixes the problem, and please don't ask me to go to an apple store because the nearest is 220KMs away.
Thanks
Maen