ADSL Modems/Routers will work only wen "Configured" with the settings of ur Broadband provider. If BSNL is giving their own Router/Modem its only bcoz they will configure it manually to set and suit ur Internet needs.
Even MTNL has its own brand of Router wich they recommend for Broad band use wich is the D-Link ADSL Router named as DSL 502T.