I cannt use phone call, mobile data network.
I can receive some text messages but usually cannot receive and send message.
I checked network status and I found the status is not very well here but my wife can use same O2 network.
I guessed this is an iphone device issue, so I bought new one. However, problems are not solved.
I would appreciate if anyone could let me know how I should do.
Some guides to help you check things and possible remedies.