On Android:
1. Open your settings app, on the top, in the search bar, type in "sim" and hit search.
2. From the results, select "SIM card lock".
3. Under the option "Sim Card Lock", click your SIM and disable the "Require PIN" setting.
4. You will need your PIN1 to unlock this- the one you received with your SIM card.
(Full path for a stock(ish) Android would be Settings/Security/SIM Card Lock. Some phone brands have this stuff hidden away, so it's easier to search for it in settings)
There, saved you a click...
I haven't used iOS in years, but I assume it would be very similar, I think they have a "search" in Settings too if I remember correctly.
