There is no global spectrum ownership, most countries regard radio waves as a national resource. ITU and related bodies only manage the standards not the allocation or ownership to operators.
What Globalstar, Iridium et al have agreements are agreements with wide array of countries but not all, for example India only allows Innmersat based devices , North Korea allows no one and so on.
OST does not cover radio frequency, only outer space( which is not well defined) ownership and activities, while the Bogota declaration failed to make progress for the equatorial countries at the UN, there are no major dispute on who owns the spectrum in the space above their national territories, most agree it is a national resource. Also to note there are many countries who are not signatories and/or not ratified the OST mostly in Africa.
Thank you for this context! Radio spectrum being considered a national resource actually makes a lot of sense. It also explains why Starlink's (residential) geographic availability map looks the way it does (i.e. corresponding to political borders).
Do you know if this is different for e.g. aviation applications or international waters? I also wonder whether Starlink (and other non-GEO operators) actually stop transmitting over countries where they don't have a license for their spectrum.
Nevertheless: Practically, Inmarsat, Globalstar, and Iridium do hold exactly these crucial L-band spectrum rights in almost all countries; Starlink doesn't yet.
In aviation, ICAO the governing body splits the globe into Flight Information Regions ( sub classified into ACCs) and delegates the management will have national member be responsible over international waters here is a list https://en.wikipedia.org/wiki/Flight_information_region
The national ICAO will "manage" practically used part of VHF and HF(pilots would use High Frequency over the ocean for greater propagation) and probably few other parts of the spectrum in this region they of course do not own the spectrum in that region.
Starlink and other communication satellites indeed will not transceive in a country without a license. In their case they transceive and not just transpond (broadcast). If any base station is attempting to connect to the satellite in a forbidden country by definition that is illegal and they will not acknowledge or open the connection.
This is why SpaceX is does not allow operations in disputed regions like Crimea, they do not want to be in position of recognizing sovereignty of disputed land for either Ukraine or Russia.
Related note: companies also don't want their civilian tech used for military applications, reason why DJI doesn't want their drones sold to either Russia or Ukraine. If they start getting classified as dual use by countries, they will be subject to export controls, sanctions etc.
What Globalstar, Iridium et al have agreements are agreements with wide array of countries but not all, for example India only allows Innmersat based devices , North Korea allows no one and so on.
OST does not cover radio frequency, only outer space( which is not well defined) ownership and activities, while the Bogota declaration failed to make progress for the equatorial countries at the UN, there are no major dispute on who owns the spectrum in the space above their national territories, most agree it is a national resource. Also to note there are many countries who are not signatories and/or not ratified the OST mostly in Africa.