hi, i bought an iphone 4s off ebay uk. i am new to iphones. seller said it was an insurance replacement for a broken 4s. the original was locked to o2 and the replacemeny might also be, but the seller never put in an o2 sim, but rather got vodafone to make it work on their network. (does that mean it must be unlocked?) the phone was reset before i received it and i could not get past the activation screen. it says "sim not valid", when i put in an orange sim card. i took it to apple and they did 'something' to it and now i can get to the menu. it says in 'about' menu in 'carrier' field: the name of whatever sim i put in (like 02 and orange) but it keeps trying to activate itself and failing and always says 'no sim' in top left of display. what does this mean? why can't it connect to a network? thanks anyone - in advance - for shedding any light on this problem.