I'm from a totally different forum; but this isn't anything much new. Carriers are beginning to roll out support for the new CMAS to mobile system, and from the looks of it ICS already supports it. Verizon for example has been rolling out a ton of updates to its Gingerbread devices to support the new mobile CMAS. Haven't seen the Galaxy Nexus get updated for that, so its either already supported or Google is just ready to blow up Verizon if they find another way to screw with a device that isn't theirs. I already forgot what forum I'm in, but I assume you all have Sprint, so all ICS devices and patched Gingerbread devices shoud have gotten this message.
I have a Sensation running ICS and I didn't get that, I'm assuming T-Mobile doesn't support this.
Hope that cleared anything up.
Sent from my HTC Sensation using XDA
