They will catch you and sue the hell out of you, everytime someone logs in, his connection details(username, ip and time) are logged by BSNL servers against the user's phone no, by checking these the guys there can find out that a connection to another guys account had been made from your phone no, boom, they get you. They actually caught a friend of mine in Kolkata:huh: .
Its very easy, they have a software named medha or something like that, all you need to do is enter the user name and all his connection details including phone nos from which connection was made will be showed on screen

, like BSNL user management screen but more detailed. And if the guy complains they will check it:no:.