(Bloomberg) — AT&T Inc. (T) is looking to sell at least $4 billion of investment-grade debt on Thursday, according to people with knowledge of the matter, weeks after it agreed to a$23 billion investment to expand its network. The telecommunications company is offering notes in as many as four parts, the people said. The longest portion of the deal, a 29-year note, may yield around 1.3 percentage point over Treasuries, the people said, asking not to be identified as details are private. Proceeds from t ...