As telecom giants AT&T (NYSE:T) and Verizon (NYSE:VZ) finish multi-billion-dollar network upgrades in the fight for new Apple (NASDAQ:AAPL) iPhone and Google (NASDAQ:GOOG) Android subscribers they've quietly seen a giant income tax windfall. Now Craig Moffet of Bernstein Research the telecom sector's most consistently bearish analyst says the tax windfall that stemmed from stimulus incentives in the wake of the financial crisis may reverse in coming years and hit the cash coffers at AT&T and Verizon. In a Monday note to clients Moffett calculates that because of the federal government's 2008 stimulus program and an accelerated depreciation taxing policy ...