AT&T Inc. is nearing an agreement to buy Time Warner Inc., a deal that would set a milestone in the converging media and telecommunications sectors and unleash a far-reaching reordering of the industry as rivals are spurred to attempt their own deals.

A deal, which could happen as early as this weekend, would unite AT&T’s wireless, broadband and satellite TV brands with Time Warner’s entertainment empire, which includes cable networks such as TNT, TBS, CNN, the prized HBO channel, and the Warner Bros. film and TV studio.

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