Thanks for the replies guys, good discussion on this topic so far.
I agree this is definitely a "macguyver" type fix, but hey if it works it works. I've been daily driving Racing's various ICS ports since the initial leak in SPITE of the caller echo issue (I just talked to everyone on speakerphone lol) so this is really welcome news to me.
As far as damaging your phone, IMHO hacking the phone and installing Rom's is just as potentially dangerous (if not more so) than taking out 6 tiny screws out and inserting a small piece of paper underneath the casing, but its everyones decision if they want to try or not.
I have verified with 4 different callers and tested myself that the fix works for me WITHOUT a case. When I put the D30 case back on my phone there is still echo. Not as bad as before, but its definitely there.
So rolling with no case is kinda annoying but I was thinking of getting an extended battery anyways so this just makes it easier
Samsung Galaxy SIII (Rooted)
Samsung Galaxy Nexus GSM
Apple iPad 3 (jb)
T-989 Galaxy SII (Retired)