Angolan investor Isabel dos Santos has launched a takeover bid for holding company Portugal Telecom SGPS in order to become a key shareholder in Brazilian telecom group Oi and reap synergies in the Portuguese-speaking telecoms sector. Dos Santos wants to link Portugal Telecom, Oi and Angolan telecoms firm Unitel if she succeeds in her bid for PT SGPS, which has a stake of around 26 percent in Oi, Mario Silva, a board member of her company Terra Peregrin said on Thursday.