Is that feasible in an iPhone? Could an iPhone with just one more radio become a sat phone?
They can already send texts over satellite so probably pretty feasible. Idk though
It's much harder at higher frequencies because you need to point your antenna more accurately. That's pretty hard to do by hand on a phone.
Alternatively, the aperture of the antenna on the satellite can be increased. So high-gain from space, but low gain on Earth, which is the approach of AST SpaceMobile.
They already have 30 GHz hardware (for 5G mmwave)!
I don’t think either spectrum will be feasible for direct to cell satellite communication in the short term, though.
IIRC SpaceMobile showed direct-to-cell satellite communication recently with 5g. Still to be seen if they or someone else (SpaceX?) can make it work large scale.
SpaceX has been launching direct-to-cell satellites for a bit now (a couple per Starlink batch), IIRC they said they need to get to ~300 such satellites to provide consistent service in at least some places. Although, again, worth emphasizing that 'large scale' in this case is still just to provide emergency coverage in places with no other coverage.
So far they have 233 DTC satellites in space, but some are still raising their orbit and not operational yet.