USSD (Unstructured Supplementary Service Data) codes are short codes used to communicate with a mobile network operator's computers. They allow users to access various services and information quickly.
1. *#06# : IMEI Information
2. *#21# : Call Forwarding
3. *#*#4636#*#* : Phone Testing ( Phone Information, Usage Statistics and WiFi Information )
4. *121# : Your Airtel Mobile Number Open With other services.
5. *199# : Your Vi Mobile Number Open With other services.