Why? Perhaps we won't see Call of Duty Onlinein the United States because Activision wouldn't benefit from cannibalizing its own share of the first-person shooter market. In China, where PCs are the most common gaming hardware, free-to-play MMOs are dominant. In the US, Activision can still expect to sell a copy of the latest Call of Duty, along with a slew of post-release content and micro-transactions to boot. We're unlikely to have a free-to-play Call of Duty in the United States so long as millions of people in the US will pay at least $60 each year up front.
Since the free-to-play day may never come, why not read Kotaku's flattering write-up?