Despite the high decibel advertising that surrounds Airtel’s 4G launch, the service is actually still only gradually taking off in the city. Bharti Airtel - which is now the third-largest mobile operator in the world - started 4G trials in New Delhi and NCR regions last month. The company left no stone unturned to push the 4G services adoption with offers such as doorstep delivery of 4G SIMs, though Airtel still has to work on the biggest concern - improving the 4G network availability. Airtel lately has been also facing complaints of frequent call drops - for which the telecom company has blamed the lack of mobile towers.