recon will become regularly available after Halo 3: ODST comes out in september. You can obtain it by completing all the vidmaster challenge achievements.
there isn't any
its something called skills
http://hubpages.com/hub/Halo-3-Armor
No, there is no armor in Halo 3 that has a knife in the shoulder.
To get security armor in Halo 3... all you have to do is get all of the original 49 achievements (you don't need the new mythic or legendary achievements).
For now, no. Although, in the near future a new kind of armor might be introduced, much like Recon armor was in Halo 3.
There is no Brute armor in Halo 3, only Elite and Spartan models.
go to http://hubpages.com/hub/Halo-3-Armor
you get all the vidmaster achievements on halo 3 and halo 3 odst
You have to get certain achievements that unlock certain armor permutations.
Technically no, the only way to wear armor in halo 3 that you can wear in reach is some of the basic armor that was already available but the new pieces of armor such as the security shoulders, sapper chest with robot arm, an gungir helmet are only available in Reach.
NO