Windows Phone 8 just got the Grand Theft Auto V companion application from Rockstar, called iFruit. The app features the same games and opportunities to interact with the PS3 and Xbox 360 game as the iOS and Android versions.
iFruit has a Tamagotchi-like mini-game where you have to feed Chop well, the GTA Rottweiler, because his growth in the app game will also translate into the main game if you log in with your Rockstar Games Social Club details.
You can get upgrades and new licence plates for your in-game cars through Los Santos Customs. In addition, you can browse the GTA version of the internet and stay connected with in-game companies through LifeInvader.
You can download iFruit from the Windows Store, but since the app just being launched, the servers could be a little busy at the moment.