After barely moving yesterday following its Q4 EPS miss, Windstream (WIN -3.8%) is selling off today in response to a downgrade to Sell from UBS. The firm thinks Windstream's dividend payout isn't sustainable, though the telco just reaffirmed its commitment to it. Windstream, which currently sports an 11.6% yield, generated adjusted free cash flow of $768M, and paid out 77% of that total in dividends. Can Windstream keep this up in the face of declining high-margin wireline voice revenue? Peer CenturyLink slashed its dividend last week.