The ATOC said number of calls to the service has reduced over the years, as now people rely more on the internet and the automated Train Tracker phone system for railway enquiries.
"Call centre operations now represent only some 7 percent of rail inquiries and this proportion continues to fall, with the internet rapidly growing in importance for passengers looking for journey information," an ATOC statement said.
It said the move to handover the rail inquiry services to the Indian firm would result in significant savings, as its internal monitoring showed that levels of customer satisfaction were the same for call centres in India and Britain.
"We can achieve significant savings by moving to one supplier and it makes sense to do so," the ATOC said.
"Passengers care that telephone and other information services are correct, useful and remain free or low cost. Where they are based is not so relevant," said Anthony Smith, Chief Executive of Passenger Focus