Shadowrun Online's payment model? The devs have posted on the game's official website in an attempt to clear things up. First of all, everyone will play on the same server, regardless of whether you choose to pay for the campaign access tier or go free-to-play.
Campaigners will receive the ability to buy every in-game item with in-game currency as well as boosts on cash, karma, and loot chances. Paying players will also apparently have more of a chance to affect the game's plot, "meaning their actions could count slightly more than the others' actions on the server in calculating what happens with the plot development."
More details are available via the full news post, including a handy chart and answers to questions like "what happens when F2P players and campaign players play together?"