US operator AT&T took the next steps in a plan to bolster coverage using satellite connectivity, by formalising a plan to lease spectrum to AST SpaceMobile to enable communication with standard mobile phones.

In a filing with the US Federal Communications Commission (FCC), AT&T noted it agreed to lease AST SpaceMobile spectrum in the 850MHz and lower 700MHz frequencies, access the operator stated is required to provide supplementary coverage from space.

AT&T offered assurances AST SpaceMobile will not begin using the spectrum until separate applications by the satellite company are approved, though their deal provides access to the frequencies 21 days after the filing, which it made yesterday (10 May).

The companies sought relevant waivers to add satellite connectivity to AT&T’s mix of mobile access technologies, along with any FCC rules which “may be necessary to permit” AST SpaceMobile’s proposed operations.

AT&T argued the arrangement with AST SpaceMobile is in the public interest, enabling it to provide services on unmodified handsets. In addition to bolstering its everyday coverage, the operator cited benefits in disaster zones.

It also asserted no “harmful interference” will result from AST SpaceMobile using the spectrum, explaining the satellite company’s constellation is being “designed to have precise control and management over downlink transmissions”.

AT&T’s leasing announcement comes a matter of weeks after the companies completed a two-way satellite voice call to a standard mobile device in conjunction with Rakuten Group.

AST has trial agreements in place with a number of big name operators but a commercial launch with AT&T would be by far its biggest success story to date.