By Anjali Athavaley NEW YORK (Reuters) - Verizon Communications Inc's announcement that it will once again offer an unlimited pricing plan marks a shift in its thinking as a price war among the four biggest U.S. wireless carriers accelerates. The biggest wireless carrier in the United States said on Sunday that it will offer an unlimited data plan for the first time in more than five years. The plan, priced at $80 a month for unlimited data, talk and text on a single line, is cheaper than AT&T Inc's unlimited plan for DirecTV and U-Verse subscribers but costs more than plans offered by smaller rivals T-Mobile US Inc and Sprint Corp .