Billionaire Mukesh Ambani’s Reliance Industries Ltd. (RIL) agreed to buy the Indian partner of Viacom for $678 million to gain news and entertainment content for its new mobile phone company. Reliance, through Independent Media Trust, will control 73.1% of Network 18 Media & Investments Ltd. and 55% of TV18 Broadcast Ltd., the Mumbai-based company said in an exchange filing.