I'll condense those to what usually is needed. You go to the service counter of the cellular provider and ask them to fix it. It's rarely your iPad that needs fixing but the account or something on their end.
I have a a IPAD2 with both WiFi and 3G. (16G) I have a contract for 3G usage.
It seems every time I need to use the 3G for internet ,as there is no WiFi service available, I keep getting a message "cannot activate cellular data". I have this turned on as well as "roaming function " from the systems applications.
Can anyone advise what to do? My SIM is correct and I do have a recognized signal from my provider.
Roku Streaming Stick 2016
Roku has the most apps, the simplest interface and the best search, making it CNET's favorite way to stream Netflix, Amazon, Hulu, HBO and all the rest.