Sprint and T-Mobile are in advanced discussions about merging, and a deal could be announced as soon as this weekend, people briefed on the matter said today.

A combination of the two companies would complete one of the telecommunications industry’s most long-awaited transactions and would create the third-largest wireless carrier in the United States, with more than 127 million customers. Sprint and T-Mobile have tried to negotiate a merger twice before.

Analysts have argued, and Sprint and T-Mobile themselves have acknowledged, that the companies need greater scale and more resources to better compete against the industry’s leaders, Verizon and AT&T.

Should the deal be completed, only three companies would dominate the market in the United States for cellphone service. It is unclear whether the transaction would get regulatory approval. A previous round of merger talks ended in 2014, having drawn strong opposition from the Obama administration.

The two companies are still finalizing details of a deal, the people briefed on the matter said. The talks could be delayed or even fall apart, the people warned.