Windstream Holdings, Inc. and EarthLink Holdings Corp. agreed to a $673 million all-stock merger, combining the network service providers as they look to trim costs amid declining revenue.

Under the terms of the deal, Earthlink shareholders will receive 0.818 shares of Windstream for each EarthLink share owned. According to Friday’s closing prices, that values EarthLink stock at $5.92 a share. That level is a 9% premium to Earthlink’s closing price of $5.42 on Nov. 3, the day before talks of a merger were reported, but below...