Activision's dev teams have outlined what Modern Warfare 2 content will carry forward to Modern Warfare 3.

MW3 will be an extension of MW2, indicating a potential cross-game future for the Call of Duty franchise. Reports indicate that MW3 was originally envisioned as a kind of expansion lacking a premium experience, but morphed into a fully-fledged $69.99 premium game as Treyarch and Infinity Ward were conscripted to assist Sledgehammer Games with MW3's development.
Although MW3 is technically it's own separate game, there will be a lot of carry-over. Well, carry-forward is more apt. This is a great win for gamers, who won't have to re-buy content or start from scratch in MW3.
"For the first time in Call of Duty's history, a vast amount of content from a previous Modern Warfare game will transfer - or "carry forward" -- and be available in the next Modern Warfare title. The content delivery is incredible: As an example, expect your available arsenal to combine weapons from both Modern Warfare titles, giving you a massive repository of armaments ready to use on day one!," Activision said on the Call of Duty website.
We've summarized how the carry-forward system works below:
- Weapons and cosmetic content will carry forward
- Wartracks will not carry forward
- Content is not retroactive - MW2 content will not carry backwards to MW3: "No MWIII content will be playable in MWII"
- MW2 carry forward content will also be available in MW3's Warzone
- Operators, weapons, blueprints, cosmetic content from Call of Duty Warzone mobile will carry forward to MW3
- Operators and operator skins will also carry over
- Timed-exclusive operators will be available, but only if you have purchased them beforehand
- All weapons and blueprints carry forward - To reiterate: If you haven't played MWII and pick up MWIII, the full complement of MWII weapons will be available, but only after the associated weapon challenges in MWIII are completed
- MW2 attachments carry forward
- Weapon camos carry forward, but MW2 camo can't be used on a new weapon introduced in MW3
- Weapon progression is cross-progression across MW2 and MW3
- Weapon charms, stickers, emblems and loading screens all carry forward