So before I've been putting up with it and now I'm fed up. It's been around 1 year and 3 different phones that I've not seen a phone number show up when I receive a call. I know for sure it is not my current phone as like I said, the last 3 phones used have had the same problem. Is this a sim problem? It's a prepaid sim on Optus. All my contacts are stored on both my sim and my phone - same problem. When I receive a call the phones displays "Unknown" as if it can't find anything. So is it my sim card? It would have to be and if so are there any ways to solve this without having to buy a new sim.