Just bought the game, and gotten about 2hrs into it.
Got to the point where I've defeated Revolver Ocelot, and got told to contact Meryl by the frequency that's on the back of the CD case. I also got handed an optical disc in game, so I thought the frequency was on that. Wasted 20 minutes and died twice before looking up a walkthrough and realise that the frequency is on the GAME DISC!!! Which obviously is not a thing if you buy the game digitally...
Seriously people, is this the way to sell a game?? At least give the bloody code as an extra with the game files!

It's actually on the GOG store page, but yeah I never liked this little aspect about the game.

Oh yeah, it's in the screenshots... I almost never look at screenshots XD

Believe it or not, I didn't realised that I had to look at CD case even back when I played it on actual PS1. I've spend quiet some time before the game decided to add Meryl's frequency in contact list. Eventually by accident I've discovered this list and was surprised how dumb that cryptic message about "CD case" was. But of course I've learned the true years later. This stupid trick does kinda make me feel dumb, almost like a barrel in Sonic 3's Carnival Night Zone.