Airtel has recently launched Huawei Modem with Latest Custom Firmware 21.157.13.00.284. When you will see in modem printed you will get Huawei E1731 only. But when you will see the inner side then you will get Huawei 173Cs-1. Huawei E173Cs-1 firmware is different from the previous one. Before this Airtel has launched modem with Custom Firmware version 11.126.16.04.284 which is not unlocked in the market. Because still Firmware 21.157.13.00.284 could not unlocked by hackers. Hardware version of Airtel E173Cs-1 is CH2E303SM. But, still we have a firmware flasher which works with this modem and it upgrade it to 21.157.13.00.910.B757. When you flash then you will be asked for a flash code. You can download Universal master code and just run this.
Put your modem IMEI Number in Huawei tab and just click on Calculate button. Now you will get Unlock code and Flash code. When you will flash your modem it will ask for a code, then provide flash code.
Now put another SIM in your modem and connect to your laptop/PC. It’s will ask for unlock code. You have already got unlock code for your modem through Universal master code. Don’t use, because it will not accept. This software generates unlock codes for 35 series IMEI number, but if will see your modem inside you will get 86 series IMEI number. I have got unlock code generator for 86 series IMEI numbers. You can see at below link.