While its importance has greatly diminished due to various satellite communication networks, the mission of the Mystic Star network still exists. MS comms aren't really heard in the clear very often, due to both encryption as well as anti-jam technology used, but every once in a while, people do hear non-secure Mystic Star comms (even if they don't know that's what they're hearing).
The SATCOM stuff is great, but because it requires so much technology & infrastructure, HF is still a necessity for major, critical comm platforms such as 'Marine 1,' 'Air Force One,' etc. & while if they use HF they'll try to utilize full-time secure voice with or without freq-hopping, if they absolutely need to they can default back to non-secure, analog single-channel HF voice like in the good old days.
As a high-school kid, I was lucky enough to have all the MS freqs & associated 'Foxtrot' channel numbers. The 'Foxtrot' identifiers were supposed to be switched around every 6 months for security reasons, but the reality was it didn't happen too often, and when it did, there was actually a pattern to it, so if you had all the freqs & heard the new Foxtrot ID's for at least two of them, it was easy to figure out the pattern.
Another cool tidbit -- back in the 1980s, Andrews AFB accessed some of the overseas remote sites (for example, Pirmasens, Germany) via non-secure, analog commercial satellite subcarriers, which could be tuned in by any TVRO nut who knew where to look & listen.