On an old sticky note taped to 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...
Read more.
Cyberpunk 2077 player finds a Witcher 3 easter egg by calling a phone number scrawled on a dingy sticky note
Source: PC Gamer (opens in a new tab)