Why am I getting the error message Not registered on network when trying to make calls?

[AC Question]

"Not registered on network"

when trying to call, getting a message "Not registered on network"

 

[SpeedyMemory]

Re: "Not registered on network"

it is easy to resolve it:
go to:
settings-> wifi and networks-> mobile networks -> networks and operators
it will search the existing operators in your location. it takes about 20 seconds.
Then select your relevant operator and that's all.