Quite a few people have asked for the "Jarheads Sound Redeployment System Mod" JSRS 1.4 to be set on the servers.
This is an awesome client mod, which changes almost all sounds in the game. You really have to hear it to belive the difference.
Currently server 3 is set to accept people connecting with JSRS 1.4 (patched). However don't worry, you can still connect with no mods! (you may notice a message about CBA Main being missing but this does not effect the gameplay/server)
To try out the JSRS sound mod (It's about 1.4 Gigabytes - but I think well worth the download) You will need to download these three things:
JSRS 1.4 mod - http://www.armaholic.com/page.php?id=11549
JSRS 1.4 patch - http://www.armaholic.com/page.php?id=15881
CBA (version 0.8.3) mod - https://dev-heaven.net/attachments/download/15957/CBA_v0-8-3.zip
[Make sure in Arma > Audio Options to set Samples to 128 to avoid sound misfires]
If you haven't using mods before, you just download and unpack into the Arma 2 Directory (for me its C:\Program Files (x86)\Steam\steamapps\common\arma 2 operation arrowhead\ as I have the steam version)
If you have a merged version of Arma 2 and Arma 2 OA. You only need the @CBA folder.
If you have a standalone Operation Arrowhead installation, you need both the @CBA and the @CBA_OA
Once you have the folders setup, in ARMA on the main menu just need to goto the Extensions page and enable the @CBA and @JSRS1.4 mods and ARMA will restart.
Any problems with the installation or connection to Server 3 let me know in the comments.