U.S. District Judge Ellen Huvelle also heard arguments about AT&T's request to dismiss the lawsuit brought by Sprint, but did not immediately rule.
Huvelle, who is hearing both the private antitrust case and the U.S. Justice Department's lawsuit to stop the deal, challenged Sprint's standing at least once during the hearing.
You don't stand in the shoes of the consumer or the Department of Justice, she said.
The Justice Department in August sued to block the deal, which would vault No. 2 ranked AT&T into the leading position in the U.S. wireless market through the purchase of No. 4 operator T-Mobile, a unit of Deutsche Telekom AG
Sprint, the No. 3 U.S. carrier, filed its own suit in September to block the deal. It complained that the mega-combination would harm its ability to obtain the latest handsets, reach roaming agreements and gain access to the market for backhaul services, links between the core network and more remote locations.
Verizon Wireless, a venture of Verizon Communications Inc
Sprint argued in court on Monday that it should have access to documents AT&T had already given to the Justice Department's antitrust division because it needs to build its own case.
At stake are AT&T's confidential documents, which likely provide an inside look at how the company views the deal with T-Mobile and how it conducts its business.
Sprint said AT&T currently has the upper hand because it already has documents that Sprint gave the Justice Department.
Huvelle declined to give Sprint the documents. I don't see it as efficient or fair, said Huvelle, in denying the motion.
Bert Foer, head of the American Antitrust Institute, said the decision is good news for AT&T because Sprint would have given the Justice Department valuable help.
There are ways in which Sprint can be exceptionally helpful to the government agencies and I'm sure that they will continue to provide advice but with more access to documents they're likely to provide better advice, Foer said.
Huvelle also heard arguments about AT&T's request to dismiss the lawsuit brought by Sprint and another one brought by C Spire, the new name for Cellular South.
Speaking for Sprint, attorney Steven Sunshine argued that if AT&T was allowed to buy T-Mobile that Sprint would have increasing trouble making deals for handsets like Apple's
If this transaction goes forward, the plaintiffs will be impaired in their ability to compete, said Sunshine.
Huvelle did not give an indication of when she will rule on AT&T's motion to dismiss Sprint's lawsuit.
Sprint issued a statement later on Monday saying a competitor has standing if it demonstrates there is a plausible case it would be harmed by the proposed transaction's effect on the market. We believe Sprint passed that test and we await the court's ruling.
Sprint's strategy is unusual in that competitors which fear mergers frequently complain vociferously to antitrust regulators but rarely file a lawsuit of their own.
Further, U.S. antitrust law is designed to protect consumers, rather than competitors, which means that courts would be expected to view a competitor's lawsuit skeptically.
Huvelle has set February 13 as the start date for trial of the government's case, and set aside up to six weeks for arguments. She will preside without a jury. The next status hearing will be on November 30.
A key government concern is that T-Mobile generally costs less than other carriers so its disappearance could mean higher prices for wireless service.
AT&T has defended the transaction, saying it would bring 5,000 overseas jobs back to the United States and enable it to expand high-speed wireless Internet coverage to 97 percent of all Americans.
AT&T has said it is keenly interested in reaching a settlement that would lead to Justice Department approval. The Justice Department has given no signs that it is interested in settling.
If the deal is abandoned, AT&T faces paying upward of $6 billion in cash and spectrum to T-Mobile.
The cases are USA v. AT&T, T-Mobile USA Inc and Deutsche Telekom AG, case No. 11-1560 and Sprint Nextel Corp v. AT&T Inc et al, No. 11-1600, and Cellular South v. AT&T, No. 11-1690. All the cases are before the U.S. District Court for the District of Columbia.
(Reporting by Diane Bartz; Editing by Tim Dobbyn)
(This story corrected the date of next status hearing in bullet and paragraph 21 to Nov. 30)