Is it possible to use an 8020 or 8100 as a music player without SIM card?

[Mastiff]

I have two phones that aren't in use, one 8020 and one 8100. I would like to have them as pure music players, but when I try, I always get to the screen with "Missing on invalid SIM card" and can't seem to get rid of that. Is there a way get around that?

[Mastiff]

Solved it myself! Putting in a SIM-card, going to Flight mode, turning off the cellphone and starring it again without a SIM-card worked! :D