"Certainly to the extent that Sprint either dropped out or wasn't interested or the government wouldn't allow it ... then T-Mobile is something that we would have an interest in," Ergen said on Wednesday on a conference call after Dish reported quarterly results.
Investors have been watching for any signs of what Ergen plans to do with the spectrum the company has spent billions stockpiling over the past few years.
Possible plans include a partnership with another wireless player or building or buying a wireless network. While its core pay TV business has stalled, Dish shares have risen more than 40 percent to $63.81 over the past 12 months mainly thanks to investors' high hopes for the value of the company's spectrum.
Late Tuesday, Sprint Corp dropped its planned bid to acquire No. 4 U.S. carrier T-Mobile U.S. Inc after regulatory hurdles proved too steep, people familiar with the matter told Reuters.
Ergen said he was not surprised that Sprint walked away from T-Mobile and called it a "smart move," considering the public resistance from regulators.
"Sometimes the best deals you do are the ones you walk away from and it takes a lot of guts to do it," he said.
Ergen said Sprint's abandoned plans for T-Mobile likely increases the options for his company, but executives have not yet discussed their plans. Still, the "announcement last night probably increased some optionality," he said.
Dish may face some competition to win T-Mobile from French telecom firm Iliad, which threw its hat into the ring with a $15 billion offer last week. T-Mobile's parent company Deutsche Telekom has shown no interest in engaging with Iliad so far.
Dish shares rose 2.3 percent, or $1.45, to $63.60 at mid-afternoon.
(Reporting by Lisa Richwine and Liana B. Baker; Editing by Lisa Von Ahn and Richard Chang)