How to use a iPhone 4 without a sim card?

I got my friends old iPhone 4 without a sim card. I just want to use it for music and apps through Wi-Fi, like an ipod touch. It's on 6.0.1 and on the screen used when regestering and authenticating your iphone. I tried to jailbreak it and it said to use redsnow but that wasn't working. Is there an easy way to bypass the authentication screen permanently, like an easy jailbreak or secret trick? (I know the call 911 and quickly hang up thing, but once your lock your phone it resets.)

You can likely find a used/ prepaid sim for very cheap and put that in. No plan required and the sim doesn't need to be valid, just enough to make the phone stop bugging you for it.

You won't be able to make calls or sms but you can easily Wi-Fi.

My iphone complains when I remove the sim but it still allows me to use it as a music player etc. I'm not sure why yours doesn't.