Sometime ago, I came across this trick for airtel which professed to find out your own number. The trick is send IM to 57070. I sent the sms and the post mentioned the number to be tollfree. Not only that I did not get my number but also my balance came down to -20. Now airtel does not give full talktime for 20 rupees. In order to make it positive, I had to shell out 30 rupees. So beware of the blogs you see and take everything with a pinch of salt!