Airtel Xstream Fiber broadband service broadband + voice service. Airtel issues fiber ONT with voip port on it which offers voice line calling service. Here any normal analog landline of used with Bsnl/Mtnl can be used.
Airtel offers HD quality voice calls with local landline number included with broadband rental. One needs compatible landline phone with RJ11 connector to connect to RJ11 port. Here is list of Cordless phone one can use with Airtel Xstream Fiber: