Lemme get this straight...
We've identified a risk that:
should someone get a root kit onto your iPhone OS device (which requires physical access, or doing something dumb like running open SSH without a unique password),
then someone could send a custom formatted text message like a blank message (which AT&T knows about and openly blocks malformed messages used for such, so the signal would have to come from a hacked SMS transmitter, not the carrier network itself),
for which they'd need to know your phone number in the first place, and have a server/deviec ready to receive the call, so obviously this isn't useful for a mass hack or botnet,
they could make your phone do simple thing like place a call (which could be traced, and which would show up in logs and call history), or enable background hardware (without a foreground app? this is at best a theory and has yet to be demonstrated as even possible).
So, if I let someone hack my device, have not synced it recently with a PC (firmware version check), someone knows my number, and sends a signal through another hacked device, then they can possibly drain my battery, or have the device make a call or send data to a traceable system. Gee, sounds like a horrible risk to me, especially since the only part demonstrated is getting a manually rootkitted device to respond to a simple signal, but they didn't actually do anything with the firmware outside of that because even still, the root kit itself is limited to the proper use of Apple's internal function calls and security model, and everything else, including how to actually get a rootkit in there in the first place, is still a thory?