When you are going in another state e.g. Delhi to Rajasthan, Haryana it may happen that your mobile failed to register on network in roaming . I faced the situation when last time I went to Rajasthan it took around one hour to register on the Roaming Rajasthan- Airtel network. My sim is a postpaid Airtel sim. At the same time our Taxi driver sim that is also a Airtel sim but prepaid working fine.
How to resolve such situation when your sim failed to register on network-
It is better to have another operator’s sim with you also a secondary cheap mobile so that you can contact in emergency. When you are going to outside forward your call to another number that is with you from the call setting as ” forward when unreachable”. When someone call you he can access you on secondary number.
You can also try this trick , most of time this trick works – switch off your mobile remove sim and battery , wait for half a minute than again insert sim and battery and turn on your phone. At this time mobile should search the network and must register.