Re: no service after upgrade to ios10
Zeusal
Enthusiast - Level 1

The symptom for me on iPhone 5 on Verizon. After restart phone will show Verizon for service with 0 signal out of 5 dots and will eventually say No Service. Unable to receive or make calls or text messages.

Go into the following:

Settings -> Cellular -> Cellular Data Options -> Roaming

then turn OFF Roaming

As soon as exiting the setting I get signal and am able to receive and send calls. I believe your theory is correct, a bug in the handshake for the network is connecting to one of the roaming providers instead of actual provider. I'm currently leaving roaming disabled to prevent recurrence. Issue with that is remembering roaming is "disabled" when I need to roam, if the phone even can roam in this iOS 10 condition.