Elon Musk's SpaceX has launched its first set of Starlink satellites to provide cell phone service anywhere in the world, the company announced Wednesday, a milestone the billionaire warned can't compete with terrestrial networks but will help plug cellular dead zones and boost global mobile connectivity.

Key Facts

Six of the 21 Starlink satellites launched on Tuesday are capable of connecting directly to cell phones, SpaceX said.

They are the firm's first ever direct-to-cell satellites and are designed to function as "a cellphone tower in space," according to Starlink's website.

SpaceX said the satellites will be first used to test its Direct to Cell service in the United States, where the company has partnered with T-Mobile.