activate iPhone without sim card
I was using an iPhone with provided sim card, but I have lost it and was using iPhone without sim card. When I updated iOS to 11, the phone is asking for activation which needs a valid sim card. I was in carrier's support center, they told me these phones aren't blocking anymore. However, It is not accepting any sim card. I have tried all operators in my area. None of them is working. What can I do with it? Should I forget about this phone?!