Access phone without entering SIM PIN
In order to unlock you need PUK(Personal Unblocking Key) code. If you have your SIM card kit, that was given to you when you purchased your SIM card then you might find PUK code on that. Since you pointed out that your phone is old so you might not have PUK or SIM kit, in that case Contact your carrier for PUK, they will ask you some details which varies carrier to carrier.
Then you have to block you PIN by entering it wrong multiple times(5-10 times) and you will be asked for PUK code. Remember, if you enter incorrect PUK code 10 times you SIM card will be blocked and you will get a message SIM card registration failed.