Telecom equipment maker Avaya Corp has announced that it had signed a multimillion-dollar five-year contract to build call centers for India's leading telecom company, Bharti Airtel (BRTI.NS), in Asia and Africa, reports Reuters.

"It is the largest deal we have ever done," Reuters quoted Ed Nalbandian, head of Avaya's managed services and contact center solutions,as saying .

The two companies have been working together on call centers in India for a number of years, but with the new deal Avaya will also implement its technology for Airtel in Bangladesh, Sri Lanka and 18 African countries.

"Getting into Africa is a big deal for them and they want to differentiate themselves there," Nalbandian said.

Airtel in 2010 acquired the African operations from Kuwait's Zain (ZAIN.KW) in a $9 billion deal that made it the fifth-biggest cellphone company by subscribers.

Avaya's technology will support over a billion calls a year and include video and social media capabilities in the call centers, he added.