Acquiring Advanced Fibre Communications Inc. last year, Tellabs became primary supplier of fiber-optic gear for New York-based Verizon Communications Inc. The other supplier: Motorola. Keeping Verizon happy is a challenge, says Robert W. Baird & Co. analyst Kenneth Muth, who rates Tellabs' stock "outperform." "You've got another Chicago-based company that's going to make your life miserable," Mr. Muth says. "If they don't keep Verizon as a customer, that acquisition will look terrible."