You can use your cell phone in game to call REAL people. You call their gamertag and you click "Hang Out" or "Invite" and then they come in to your world and the multiplayer experience begins. At least that is how it was in August.
Also here is a confirmation of Microtransactions:
http://www.kontrolfreek.com/blog/gta...nsactions-duh/
Luckily it's overpriced so most people won't be buying them. Just 1 good heist can get the most expensive card.