On an old sticky note taped to pg168 ทางเข้า a wall early on in Cyberpunk 2077: Phantom Liberty is a phone number you can call that will connect you with the past. Real Witcher heads should recognize the fuzzy music coming out of the phone instantly as the Witcher 3's main theme.
The reference to CD Projekt's other RPG series is easy to miss. There are a number of scribbled numbers on the wall that you can punch in, but only one of them seems to give you a little taste of The Witcher 3.
Reddit user MayorMayNotBeSitting found the reference earlier this week and I went and confirmed it myself. Sure enough, if you call "5745552377" on the phone in the Capitán Caliente restaurant, the song will play and Johnny Silverhand will give you a little grin and thumbs up in approval. ทางเข้า w88 ใหม่ ล่าสุด If you've already moved on from that part of the story, you can still head back and dial the number whenever you want.
I tried the other numbers and could only get "Never Fade Away" from the Cyberpunk 2077 soundtrack to play. The phone number for CD Projekt's office didn't do anything either. I could probably spend way too long trying numbers out, but I'm going to assume the two songs are the only secrets there.
Tried one of the numbers on the wall. from r/cyberpunkgame
Cyberpunk 2077 has several references to the Witcher. Most notably, there's a magazine with Ciri on the cover in the Corpo lifepath intro. You can find an arcade machine with a game called "Roach Race," referencing Geralt's horse, and Johnny Silverhand even plays the main theme from the Witcher 3's Blood & Wine expansion on guitar at one point. Hearing the Witcher 3 theme isn't as wild as playing a functioning Doom clone, but it's a cute nod to CD Projekt's past nonetheless. I'm also going to take it as more evidence that there's a connection between both universes after hearing Ciri tell Geralt about visiting a world with cyborgs and flying ships.