DSL Modem/ wifi Router

Hi Friendz,
I need a wifi router with modem which can be also used later as wifi router for cable broadband.
Its for my dad, he is currently using BSNL which but later he will take cable broadband next year. So I need a wifi router which can be used as a modem for the remaining year, then it can be used as wifi router for cable broadband (Alliance).

I don't have much knowledge on networking. Please help me.

Thanks.