UPDATE 1-Oi bondholders hire Moelis for restructuring talks -source

SAO PAULO, March 24 (Reuters) - A group of unidentified Oi SA bondholders has hired Moelis & Co to advise on a plan by Brazil's most indebted phone carrier to restructure part of its 55 billion reais ($15 billion) in obligations, a source with direct knowledge of the matter said on Thursday.