Activist investor Elliott Management has taken a $3.2bn stake in AT&T, one of its largest-ever positions, and is pushing for a strategic overhaul at the US telecoms group, which it says has been a “disappointing investment for shareholders”. of Time Warner, saying the US telecoms group has embarked on a “questionable” acquisition strategy. In a letter to AT&T’s board of directors on Monday, Elliott outlined a four-part plan to tackle what it described as the company’s long-term underperformance, citing a number of strategic setbacks that include its failed bid to buy T-Mobile for $39bn in 2011 and lack of direction since acquiring Time Warner.