You've given us no details to base any diagnosis off of. What device? OS and version? Is the SIM good? Have you tried it in another phone? Have you tried another SIM in the phone that is not working? Is it a new SIM? Is it a new line of service? What country and carrier? What happens when you try to make a call? What error messages are seen? What happens when someone tries to call you? What do they hear?
Is your bill paid up with your carrier??????????
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