would have been great if existing SIM and plan could be used in this device
Most imp T&C
"7. What are the connection plans available in Airtel Xstream AirFiber?
Airtel Xstream Fiber comes with a 6 month plan which allows users to enjoy 100Mbps speeds at Rs. 4,435 (exclusive of GST). There is also a one-time refundable security deposit of Rs. 2500 on the device."
So speed will be restricted to 100 Mbps