Have you tried more than one sim card? Actually, the problem could be from the phone. It could be a defect. Nothing to do with whether the carrier supports it or not. If there's a sim card in there then it shouldn't say " Sim not detected"
Sent from my Nexus 5 using XDA Premium 4 mobile app
Nexus 5 - 32GB - D820 - latest 4.4.4 Mahdi ROM with Franco's Kernel
Sony Xperia Z Ultra - C6833 - White - Latest stock rom and kernel - rooted with Dual Recovery.