Not sure if this will end up in right place but... I bought a used mobile. Have done checkmend and the serial nos are ok etc. It's a sony xperia arc on 02. My sim is 02. Just shows as not connected to a network and says "your sim is not able to connect to the network". When I put a sim card in it comes up with "sim unlock network pin" with a box for you to put in the pin. Can anyone explain what the problem is? Is there hope? Thanks (by the way the phone is v nice, camera looks good, but not much use if I can't make calls or get online!!!).