We are haveing problems with both our phones - a Samsung GT-B3310 where the problem is "Invalid Sim Card" and a Samsung SGH-E250 where the thing is saying "Network Lock". We do not have any code that fixes this (and we've tried all the numbers we can find).
Both phones were purchased from a Virgin shop - I think that both were from the Liverpool outlet but I no longer have the till receipts.
I've refitted both phones with the sims I had remeoved and both still work. This is important to us as we need them for emergency use for health reasons.