Airtel has launched 4G in India. But in the market there only few smartphones or devices support 4G. iPhone is one of the smartphones which support. But do you think your iphone will work with Airtel 4G? iPhone 5s, iPhone 5c, iPhone 6 and iPhone 6 Plus support 4G. But condition is you must have purchased these iPhone from Apple Store in India. It should not be imported to India.
Yes, you read it right. If you have someone has gifted you iPhone from Outside India, 4G will not work on that iPhone. Reason is 4G is India having different frequency than other countries. Because of frequency mismatch 4G will not work in imported models of iPhone.
If you want to check whether your iPhone is compatible to Indian 4G, then just check the model number of iPhone 5s or iPhone 5c at the back. In case of iPhone 5s, it should be A1530 and in case of iPhone 5c, it should be A1529, only then 4G will work in India in your iPhone. If it is something else, there are chances that Airtel 4G will not work.
In India, Airtel has launched 4G service at 2300 MHz. Very soon, Reliance 4G is going to be launched and everyone is expecting that Reliance 4G will work with all iPhone models no matter from these have been purchased because Reliance is expected to launch 4G at the frequency of 1800 MHz.