I have an old iphone 5 I want to just use as an ipod so I can take it to the gym and not worry about my regular phone getting stolen from my locker. I put an unactivated SIM in so I could use it, but it keeps popping up with the "iPhone not activated" error all the time. Is there a way to get rid of that from popping up? I don't have service and don't want service on it.