I have an Airtel UP East sim and today I accidently discovered a cool feature. Using this trick you can keep your phone turned on and whoever calls your number will be intimated that your number is switched off. And you will even get an SMS with the number of caller so you will get to know who is calling you. This feature can come handy sometimes when you want to use your phone for outgoing or internet browsing without letting anyone disturb you. Also in situations when you have a fight with your significant other and you want to see them trying to call you madly, without turning your phone off. The trick is to go into your phone settings and inside that navigate to call settings then call forwarding or call diverting. Set your phone to divert all calls to the number 9935044567 and viola! Whoever calls you will now be informed that either your phone is switched off or not reachable. Also, you will receive an SMS in a few moments from the caller's number. If you are an Airtel customer of some other circle then too this trick will work but you have to change the number. The number can be obtained easily by going to call divert or forwarding settings and seeing the preset number for the field Divert when not reachable. Set that same number to Divert always and you are done! I tested with my Reliance GSM number of UP east and set its divert to that Airtel number 9935044567 and w00t!! When anyone calls my Reliance number he/she is told that This airtel number is not reachable! ROFL! Its fun and useful at times! Do try it.