It’s not the phone. It’s the carrier you are using. The phone may not accept the carrier you are trying to use with it. I.E., sprint and AT&T aren’t compatible networks, so the phones are a little different, as with Verizon as well. So the phone isn’t the issue, it’s the SIM card that is being used. You may have to switch network providers or get a different iPhone that will work with your networks carrier. I am on ATT myself and I cannot take this phone and switch to Verizon as they run a different type of equipment that is not compatible with ATT’s network. Hope this makes sense.