Copying this comment from my response to you +Ray Dull
The patch: http://review.cyanogenmod.com/#change,7535
I would like to clarify that patch; but first a little history before that patch existed. Prior to that patch (which borrows code from the Nexus S); all e911 calls would fail, either by pushing the phone into airplane mode, or simply silently dropping the call. As the patch is titled, it did indeed fix e911 calling (emphasis on calling) for the SGS devices (aries based). However, even with that patch, the e911 calls made on Vibrant (in combination with Tmobile) would complete the call, but without audio. This becomes a situation where, if a 911 call is made, and the operator cannot hear the other end, they will assume the caller is unable to speak, thereby dispatching emergency services (which incidentally, Android sends GPS data along with e911 calls – which is also wonky, to say the least, on the Vibrant as a platform)
As for the patch itself, I have asked a CM team member to add a comment to further clarify.