Shares of the country's second-largest telecom operator fell as much as 2.3% to 537.25 rupees in morning trade and were set for a fifth straight session of losses.
The company's quarterly average revenue per user (ARPU) at its India mobile services business rose 7.4% to 145 rupees from a year earlier, but dropped nearly 13% from the previous quarter.
Analysts at Jefferies had expected Airtel's India mobile ARPU for the fourth quarter to be 152 rupees. The company did not give details on the sequential drop, but has a call with investors scheduled later in the day.
The drop comes after the Telecom Regulatory Authority of India's guidelines to abolish https://www.reuters.com/article/india-telecoms-idUSL4N28R3HS interconnection usage fees, which operators pay each other for calls made from one network to another, were implemented from Jan. 1.
Rival firm Reliance Jio, controlled by billionaire Mukesh Ambani, had reported ARPU of 138.2 rupees per subscriber per month for the March quarter - a sequential drop of about 9%.
Bharti Airtel posted a consolidated profit of 7.59 billion rupees ($103.83 million) for the quarter ended March 31, compared with a loss of 52.37 billion rupees a year earlier.
It added 14.1 million subscribers in India during the first three months of 2021, growing its base to more than 350 million, while bigger rival Reliance Jio added 15.4 million net subscribers in the quarter to reach 426.2 million subscribers.
Bharti Airtel's revenue from operations for the quarter was 257.47 billion rupees, nearly 12% higher than 230.19 billion rupees the previous year.
($1 = 73.1030 Indian rupees)
(Reporting by Shivani Singh in Bengaluru; Editing by Ramakrishnan M. and Devika Syamnath)