send national free sms through airtel for free

Since there is many way sending free sms through airtel connection. But many tricks wont work in certain places.I have found that now we can send 50 free sms for 5rs. In order to workout this you have to activate separate service. This service can be used only by airtel users and it doesnot works with airtel life time users. What you have to do is just send SUB5 to 170 and a short while service will activated and start using the service.