It seems that Los Santos is still hiding some never-before-seen Easter eggs. As discovered by Twitter user @KarmaIngram1, there's actually one more secret phone number in GTA V that you can call. Dialling 1-999-367-3767 connects you to "Black Mobile phones," which for whatever reason triggers an explosion, and it also changes the appearance of your mobile phone itself. You can see this in action in the video above.
It's kind of random, to be honest. Still, it's enough to have reinvigorated the never-ending search for the ultimate mystery in GTA V. Players are trying to figure out if this number connects to anything else in the game -- which naturally means trying to make the explosion connect with a UFO, among other things.
Its unclear how long this has been in the game, but it's worth noting that when people data-mined GTA V a while back for secret mobile phone numbers, this wasn't one of the numbers players found within the game. It could be that Rockstar patched it in recently -- remember that Bigfoot thing from 2015?