Yes there is a way!
Call of Duty 4 makes you unlock weapons, weapon attachments and mods, camouflage, and challenges. Well there is a way around that because all of the data is stored client-side. To unlock all weapons for Call of Duty 4 multiplayer so that you dont have to level up follow these easy instructions.
1. Download this mpdata file.
http://www.filedropper.com/mpdata
2. Go to Call of duty Multiplayer and then Options then multiplayer options then click "key code"
3. Save the key in notepad
4. Then go back to the multiplayer game and replace the key that you just saved with: DL2J8PY44Q22GE4888D22
5. Press OK and quite the game.
6. Navigate to your Call of Duty 4 profile folder usually ~Applications/Call of Duty 4/Call of duty 4 Data/players/profiles/what ever your multiplayer name is/
7. Place the mpdata file you downloaded in your user name folder (replace the one already there)
8. Open the COD4 MP game and check your rank. You should now be level 55 with all challenges, guns, and every camouflage unlocked!
9. Finally, in the game go to Options -> Multiplayer Options -> Key Code and type your original cd key you have saved in notepad. (THIS IS VERY IMPORTANT)
There you go, you now have everything unlocked. Enjoy,
Kent