On Sunday, Sprint Corp. and T-Mobile US Inc. announced a merger that could transform the U.S. telecommunications sector. And more than a few lawyers from Am Law 100 firms are involved behind the scenes trying to smooth the way for a transaction not expected to close until the first half of 2019.

The proposed $26.5 billion all-stock deal will see Bellevue, Washington-based T-Mobile, which is owned by Deutsche Telekom AG, take control of Overland Park, Kansas-based Sprint, a majority stake of which is owned by Japanese conglomerate SoftBank Group Corp. If the merger receives shareholder and regulatory approval, the combined $146 billion company will create a U.S. telecommunications rival to industry leaders AT&T Inc. and Verizon Communications Inc.