The Airtel mobile service provider has certain technical problems. One of my Airtel SIM card shows the same problem as you have mentioned. Sometimes its network reception tower is not displayed on mobile and if I call the customer service center then it shows the network tower on the mobile display. Hence, I too would like to mention that airtel mobile services are not working fine.
The Uninor Telecom Company has brought various talk time schemes and many of them are too good. But I would like to suggest that if you stay out of city then you need to think over using the Uninor mobile service. Because I have seen that at times Uninor goes out of coverage area. Hence, if you live in city then you will not face any problems but if you stay outside city then it's not good to rely of Uninor. They are improving a lot. Hence, choose wisely.
Have a Nice Day.
"Don't Worry about Results, Its time to Perform every now and then" - Pravin Chavre.