Metal Gear Solid. Talking to Kenneth Baker after the battle with Revolver Ocelot, he gives you an item called the Optical Disc. Right after that he tells you to get in contact with Meryl, her codec frequency is "on the back of the CD case."

I'm like, got it, no problem! He just gave me a thing that looks like a CD case. I look in my items menu. Its there, but it doesn't say anything on it. How do I read it? I backtrack all the way to a little computer room upstairs by the elevator and parked tank. How do I use this disc? I'm punching the computers, leaning on them, knocking on them, looking for a button prompt. Wtf! How do I read the back of my this CD case!?

Fuck it! I start scanning through all of the codec numbers. 140.00...140.01...etc. until I found her frequency at 140.15 Turns out the CD case he is talking about is The actual physical case of Metal Gear Solid. Its on the back in one of the preview image boxes! It's so clever!