It won't harm the phone, but it won't work either. You can find generic SIM card that you can program yourself, but that's not what is used in a phone. Your pho

It won't harm the phone, but it won't work either. You can find generic SIM card that you can program yourself, but that's not what is used in a phone. Your phone will only work with a SIM card embedding specific applications called SIM for 2G (that's where the name comes from as you see, the physical thingy is named UICC) or USIM for 3G/LTE. And this application embeds security components that will authenticate the card to the operator, either as a direct customer or as a customer of another telco which is a roaming partner. If this authentication fails, you'll have no access. If there's no valid SIM or USIM application your phone modem won't do anything with the card.