For the second day in a row, AST SpaceMobile (ASTS 19.77%) stock is hopping.

AST shares tumbled earlier this week after the company floated $460 million in dilutive convertible debt to raise cash for building new direct-to-cell satellite communications satellites. Yesterday, however, AST stock posted a win after customer Vodafone placed "the world's first video call via satellite using a standard smartphone from a remote location" -- and used an AST satellite to do it.

And today? Today AST stock is flying 17.5% higher through 10:15 a.m. ET, and recouping all its losses from earlier in the week. Why? The Federal Communications Commission has just approved AST to begin testing its satellites in the United States.

AST's big news

This latest news (from AST SpaceMobile) isn't entirely new. Last week, PCMag was first to report the FCC had granted AST "Special Temporary Authorization," or STA, to begin testing its satellites with U.S. partner AT&T.

What is new about today's announcement, though, is that the FCC STA actually permits AST to test its satellites with both of its biggest customers -- not just with AT&T, but with Verizon Communications, too.

All of AST's five BlueBird satellites in orbit will be involved in the testing, which will provide "non-continuous cellular broadband service across the United States and in select markets globally." The company says the five satellites can provide the equivalent of 5,600 "coverage cells" in the United States. It's not clear how many users the satellites can support, but with terrestrial cell service, for example, the rule of thumb is that each cell tower in a coverage cell can support about 30 simultaneous callers.

Is AST SpaceMobile stock a buy?

AST Global Head of Regulatory Affairs Vikram Raval called the FCC's decision "a pivotal moment," and Chief Commercial Officer Chris Ivory said the STA will "accelerat[e] our path to commercial activity." And the news does sound good. Still, questions remain. How many customers can AST really service? And when will beta service begin?

Basically: When will AST move beyond testing, and start making money?