Elon Musk wants SpaceX (SPCX) to take on America's largest cell service providers, but matching the telecom giants' vast wireless networks could take years and billions of dollars, executives and analysts warned this week.

SpaceX, which already operates the world's largest commercial satellite network with Starlink, is in talks with major telecommunications infrastructure companies to secure access to at least 80,000 cell sites across the United States, Bloomberg reported. The move would advance Musk's ambitions to establish a fourth nationwide wireless carrier alongside the three traditional telecom and mobile service incumbents: Verizon (VZ), AT&T (T), and T-Mobile (TMUS).

The announcement sent stock in AT&T and T-Mobile falling by as much as 6% on Friday, while Verizon declined by a thinner 1.5%.

Satellite launches through Starlink and spectrum acquisitions "will pave the way for Starlink Mobile to become a major mobile carrier in the US," Musk said on SpaceX's earnings call.

But breaking into an industry whose dominant players have spent decades building out infrastructure, acquiring spectrum, and cultivating millions of subscribers will be no easy feat.

"It's not something that gets done overnight," AT&T CEO John Stankey told analysts on his company's earnings call Wednesday, before the latest details of SpaceX's plans emerged. "It takes a lot of years and a huge level of investment to get to the kind of performance levels that customers have become accustomed to in scaled networks."

SpaceX's tower negotiations, which reportedly include cell tower operator Crown Castle (CCI), represent one of the clearest indications yet of the scale of SpaceX's ambitions. They also illustrate the substantial financial and technological barriers facing Musk as he attempts to challenge America's entrenched telecommunications giants.

The company's reported target of 80,000 cell sites would put its planned network on a scale comparable to that of the three incumbents. Verizon, AT&T, and T-Mobile each lease space on approximately 60,000 to 80,000 US cell towers combined, according to Goldman Sachs analysts, while the country has roughly 175,000 traditional cell towers nationwide, per data from SNL Kagan.

The cost for such a build-out would be immense, even for a company with the capitalization and balance sheet of SpaceX. The average cellular tenant pays roughly $50,000 per year to lease space on a cell tower, according to Goldman Sachs analysts led by Michael Ng. At that rate, an 80,000-tower network could generate approximately $4 billion in annual rental payments, or between $20 billion and $40 billion over a typical five- to 10-year leasing period.