You must have notice that Whenever you insert a SIM card other then Bsnl in your Bsnl 3G Data Card and open the BSNL 3G program to access internet on your computer, a massage appears and says that "Invalid SIM" then the application closes.It happens because BSNL 3G Data Card does not support other SIM cards like Airtel, Aircel, Vodafone, docomo etc. only you have to use BSNL SIM cards.
But don't worry about that, now you can use other SIM cards in the BSNL 3G Data Card by doing some Registry settings on your computer. This Trick will work on any version of Windows.I have tested the trick on Teracom BSNL 3G Data Card LW273 and it's working fine. Just follow the steps below.
Go to your Registry Editor (Start ->Run Type regedit then press Enter)
Double click on HKEY_LOCAL_MACHIN then SOFTWARE
Now come down and click on Linktop3G
Then Double Click on Engineer from the right panel
Change the default Value data from 1 to 0 then click OK and close the Registry Editor.
Then close the BSNL 3G Application and check the process if the BSNL 3G.exe is running then end the process or simply you can Restart the Computer.
Now the Bsnl Data card is unlocked, put any operator SIM in your BSNL 3G Data Card and open the application it will not show any error message.
How to access internet using it, here is the example for Aircel SIM
Open the BSNL 3G Application
Click on Settings then click on Connection
Click on Add to Add New Profile
Profile Name - Aircel
Number - *99***1#
User Name - None (should be empty)
Password - None (should be empty)
APN - aircelgprs
Click on Apply then click on Set Default
Now click Connect button to get connected to the internet.
HERE IS THE SETTINGS FOR OTHER OPERATORS