ok, so my sister was locked on a contract with telsta; the contract ran out and she got a new phone and gave me her old iphone, im with optus pre paid and she told me that the sim should work because it is no longer under contract, so i put my sim in and it said invalid sim card, so i took it into telstra and they gave me a number to ring to get it unlocked, so my sister rang and got it unlocked, and told me to wait 24 hours; it has now been 3 days and it is stuck on the 'emergency call' screen and when i put my sim in it tells me to plug it into itunes, and when i do; it tells my my sim is still invalid what do i do to the phone ?