Here's a strange one. The problem is actually with my Nokia 720, but I suspect a more general problem. I'm currently visiting Kinshasa, Democratic Republic of Congo. When I stick a local SIM in my phone, I get an invalid SIM error. When I stick the same SIM in another (none Windows) phone, it's fine. I don't think it's a hardware problem with the 720 since my UK, Namibian and Zimbabwean SIMs still work with it. Any ideas?