Please share your experience in a short survey to help us identify how we could improve these pages and better assist you in resolving the problem with your device. Thank you for your help!
Are both SIM cards active at the same time on my Nokia device? - Nokia FAQ
Both SIM cards can be connected to the network at the same time, but while one SIM card is active, for example, making a call, sending or receiving a message, or transferring data, the other is unavailable.