NEW YORK (AP) — An antitrust suit aimed at blocking T-Mobile’s acquisition of Sprint opened Monday in a crowded courtroom in New York with testimony from Sprint executives that touched on the consumer benefits of the company’s competition with T-Mobile and other carriers.

A group of 14 state attorneys general, led by New York and California, aim to convince a federal judge that the $26.5 billion deal should be blocked. T-Mobile has already notched approvals from key federal regulators, setting up an unusual situation where states officials are seeking to overturn their federal counterparts.

The trial, in U.S. District Court in New York, is expected to last several weeks.

If T-Mobile prevails, the number of major U.S. wireless companies would shrink to three from four. A combined T-Mobile-Sprint would become a fiercer competitor to larger Verizon and AT&T. But the states argue that having one fewer mobile carrier would reduce competition and cost Americans billions of dollars in higher phone bills.

T-Mobile and Sprint provide cheaper alternatives to Verizon and AT&T, and T-Mobile has branded itself the “Un-carrier,” one that has made consumer-friendly changes such as bringing back unlimited-data plans and shattering two-year service contracts. There are concerns that less competition would put an end to these types of changes, although T-Mobile says that won’t happen.

The states’ lawyers on Monday questioned Roger Sole, Sprint’s chief marketing officer, and Angela Rittgers, the senior vice president for sales and marketing for Sprint’s prepaid brands, Boost and Virgin. Their aim: Demonstrate that Sprint and T-Mobile competed with each other for customers by cutting prices and bringing unlimited plans back to the wireless market, benefiting consumers.

In one example, they showed an email from former Sprint CEO Marcelo Claure to Sole, saying Sprint had to match a buy-one-get-one-free offer from T-Mobile for the iPhone 8. “We have no choice,” Claure said.

T-Mobile, which promised not to raise prices for three years, defends its deal as good for competition. It repeats previous arguments that the combined T-Mobile and Sprint will be able to build a better 5G network — a priority for the Trump administration — than either company could manage on its own.