NEW YORK (AP) — T-Mobile CEO John Legere said if his company's $26.5 billion deal to buy Sprint fails, it may have to raise prices to slow user growth and relieve stress on the T-Mobile network. He said that would be his "worst nightmare."

Legere's testimony came on the fourth day of a high-profile antitrust trial. Fourteen state attorneys general are suing to block the combination of T-Mobile and Sprint. They say the deal would cost consumers billions.

The trial with the states is a major hurdle for T-Mobile, but federal regulators have already cleared the merger. The Justice Department appro...