Pivotal Research Group launched coverage on Verizon Communications (VZ), AT&T (T), CenturyLink (CTL) and Frontier (FTR), and rated the nation's two biggest phone companies at hold and the two smaller carriers at buy. Steve Sweeney, Pivotal's telecom analyst, said that with the recent run-up in shares of Verizon and AT&T, the stocks look fully valued at current levels. Shares in AT&T have gained 23% since Jan. 27, while Verizon is up 18% in that