Dial 1503 from your BSNL number
Dial 123 from your BSNL number
Dial *1# on your BSNL SIM
Dial *222# on your BSNL SIM
Check the SIM card pack or welcome letter
Check your BSNL account or app if registered
Call another phone from your BSNL SIM and see the caller ID
Send a missed call or SMS from your BSNL number and check the received number on the other phone