Sec

I know that you have to register your phone specially to use it in russia, but I have no idea if that actually affects reachability.

I know Iridium is illegal in Kuba, but works just fine there.

I don't recall any restriction in china, currently.

If you have an SDR at hand and want to try it yourself, get the code from GitHub https://github.com/muccc/iridium-toolkit Even with a simple WLan antenna you will get some reception outside (preferrably on a roof).